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![Mo\ \Ti binary alloy phase diagram [22].](profile/Liang-Liang-Zhang-2/publication/331468935/figure/fig1/AS:748987615309825@1555583971630/Mo-Ti-binary-alloy-phase-diagram-22.png)
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![Fig. 1. Mo\ \Ti binary alloy phase diagram [22].](profile/Liang-Liang-Zhang-2/publication/331468935/figure/fig1/AS:748987615309825@1555583971630/Mo-Ti-binary-alloy-phase-diagram-22_Q320.jpg)
Molybdenum has tremendous application potential in the nuclear power field, but its application is limited by the grain-boundary embrittlement of fusion-welded joints made of it. In this study, titanium was selected as an alloying element to reduce brittleness of laser weld beads in molybdenum “cladding-end plug” socket joints. Brazing was also per...
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... layer on the Mo grain-boundary surface, thereby reducing the grain-boundary strength [20]. Considering the deficiencies in the above mentioned elements and based on the selection criteria for alloying elements introduced in the previous paragraph, Ti is found to have notable advantages. First, no brittle phase is formed when mixing Ti and Mo (Fig. 1); Ti and Mo are infinitely miscible in one another at high temperatures. Second, Ti can easily combine with O [15,21], thereby reducing the content of free O in Mo. Moreover, because the solidification temperature of Ti (1670 °C [22]) is far lower than that of Mo (2623 °C [22]), Ti is prone to crystallize at the Mo grain boundaries and ...
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... are explained from phase transition and energy perspectives. First, the O in the base metal and shielding gas could enter the welding pool during the welding process as the impurity element. In addition, the melted Ti foil is evenly distributed in the welded zone as a result of the stirring action of the welding pool (Fig. 3 (b); S1, S2 and S3 in Fig. 10). Owing to its low melting point (1670 °C), Ti is transported to the Mo grain boundaries during the crystallization process [23]. Considering the high cooling rate (200-500 K·s −1 ) of the welding pool, some Ti could form a solid solution inside the Mo grains [42,43], and the majority of the O is precipitated at the Mo grain boundaries ...
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... Owing to its low melting point (1670 °C), Ti is transported to the Mo grain boundaries during the crystallization process [23]. Considering the high cooling rate (200-500 K·s −1 ) of the welding pool, some Ti could form a solid solution inside the Mo grains [42,43], and the majority of the O is precipitated at the Mo grain boundaries [5,7] (S4 in Fig. 10). As the temperature of the welding pool decreases to approximately 2300 ± 150 °C, the MoO 2 phase could be firstly precipitated at the Mo grain boundaries (S5 in Fig. 10). When the temperature drops to 1870 °C (the solidification point of TiO 2 [22]), the Ti solid solution in the Mo grains combines with O, forming TiO 2 [15,21,22]; in ...
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... K·s −1 ) of the welding pool, some Ti could form a solid solution inside the Mo grains [42,43], and the majority of the O is precipitated at the Mo grain boundaries [5,7] (S4 in Fig. 10). As the temperature of the welding pool decreases to approximately 2300 ± 150 °C, the MoO 2 phase could be firstly precipitated at the Mo grain boundaries (S5 in Fig. 10). When the temperature drops to 1870 °C (the solidification point of TiO 2 [22]), the Ti solid solution in the Mo grains combines with O, forming TiO 2 [15,21,22]; in addition, the Ti precipitated at the Mo grain boundaries combines with O, forming TiO 2 , and some surplus Ti at the Mo grain boundaries could cause the reduction of some ...
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... °C (the solidification point of TiO 2 [22]), the Ti solid solution in the Mo grains combines with O, forming TiO 2 [15,21,22]; in addition, the Ti precipitated at the Mo grain boundaries combines with O, forming TiO 2 , and some surplus Ti at the Mo grain boundaries could cause the reduction of some MoO 2 at the Mo grain boundaries [44] (S6 in Fig. 10), thereby reducing the MoO 2 content at the Mo grain boundaries. Eq. (1) shows this reduction reaction. At a temperature lower than 1870 °C, the free energy of this reduction reaction is b0 (eq. (2), eq. (3) [46], eq. (4) [46], eq. (5) [44], eq. (6) [44]) and, from a thermodynamic perspective, can take place spontaneously [45]. Table 4 ...
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... tensile strength of the Mo-0.03Ti-B joint alloying by method B was the same as that of the base material (Fig. 7(a)). The backscattered electron (BSE) image of the cross-section of the Mo-0.03Ti-B joint (Fig. 11(a)) shows that a metallurgical bonding zone (MBZ) was formed at the location where the Ti foil was pre-placed in the HAZ. The composition of the MBZ exhibited a notable gradient variation in the axial direction (AD) of the Mo tube. The thickness of the MBZ, which is within 800 μm of the welded zone, was greater than the original thickness ...
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... Mo 38.103wt%-Ti 61.658wt%, respectively. In other words, the farther away from the weld bead, the higher content of Ti was in the MBZ. The EDS line-scanning of sites B and C in the MBZ ≤ 800 μm away from the WB also show that Mo and Ti were evenly distributed along the whole metallurgical bonding interface in the radial direction of the Mo tube (Fig. 11(c) and (d)). The MBZ ≤ 800 μm away from the WB was composed of a mixture of Mo and Ti and N30 μm in thickness, and hence is defined as a mixed melting zone (MMZ). The middle layer, which is 1200 μm away from the welded zone, contained 99.901 wt% Ti and was as thick as the original Ti foil. Thus, this zone was the original Ti foil ...
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... the mechanism of formation of the MMZ is analysed. The MMZ contained a high Mo content, which gradually decreased as the distance in the AD from the fusion zone increased (Fig. 11(a)). Mo had two possible sources: (1) the melting of the Mo rod and tube on the two sides of the interface of the MMZ and (2) the Mo contained in the welding ...
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... sources of Mo in the MMZ were analysed using the zirconium (Zr) tracing method, as shown in Fig. 12(a). The results show that the WB and the MBZ ≤300 μm away from the welded zone both contained significant amounts of Zr after welding (Fig. 12(c)), suggesting that the Mo in the MBZ ≤ 300 μm away from the WB came partially from the welding pool. In addition, the thickness of the MBZ ≤ 300 μm away from the WB ranged from 60 to 50 μm, ...
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... sources of Mo in the MMZ were analysed using the zirconium (Zr) tracing method, as shown in Fig. 12(a). The results show that the WB and the MBZ ≤300 μm away from the welded zone both contained significant amounts of Zr after welding (Fig. 12(c)), suggesting that the Mo in the MBZ ≤ 300 μm away from the WB came partially from the welding pool. In addition, the thickness of the MBZ ≤ 300 μm away from the WB ranged from 60 to 50 μm, significantly greater than that of the Ti foil (30 μm), indicating that the Mo rod and tube on the two sides of the interface also melted. The ANSYS ...
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... μm away from the WB ranged from 60 to 50 μm, significantly greater than that of the Ti foil (30 μm), indicating that the Mo rod and tube on the two sides of the interface also melted. The ANSYS simulation results for the temperature field during the welding process show that the maximum temperature at site B (250 μm away from the welded zone) in Fig. 11 (a) ranged from 1670 to 2623 °C, and the Ti foil could be melted with this temperature range. In addition, based on the infinite mutual miscibility of Mo and Ti, shown in the phase diagram in Fig. 1, a large amount of Mo at the Mo rod-Mo tube interface melted and entered the liquid Ti [47]. Thus, the Mo in the MMZ 0-300 μm away from ...
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... results for the temperature field during the welding process show that the maximum temperature at site B (250 μm away from the welded zone) in Fig. 11 (a) ranged from 1670 to 2623 °C, and the Ti foil could be melted with this temperature range. In addition, based on the infinite mutual miscibility of Mo and Ti, shown in the phase diagram in Fig. 1, a large amount of Mo at the Mo rod-Mo tube interface melted and entered the liquid Ti [47]. Thus, the Mo in the MMZ 0-300 μm away from the WB came partially from the Mo rod and tube melted at the interface and partially from the welding ...
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... metals in the welding pool were unable to enter the zone 300-800 μm away from the WB. However, the Mo content at points 3 and 4 in Fig. 11(a) was as high as 54.554 wt% and 38.106 wt%, respectively. Theoretically, Mo could only come from the melted base material on the two sides of the interface. The ANSYS simulation results show that the maximum temperature at site C (Fig. 11(a)), which was 700 μm away from the WB, was N1670 °C, meeting the condition for the melting of the ...
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... pool were unable to enter the zone 300-800 μm away from the WB. However, the Mo content at points 3 and 4 in Fig. 11(a) was as high as 54.554 wt% and 38.106 wt%, respectively. Theoretically, Mo could only come from the melted base material on the two sides of the interface. The ANSYS simulation results show that the maximum temperature at site C (Fig. 11(a)), which was 700 μm away from the WB, was N1670 °C, meeting the condition for the melting of the Ti foil. The melted Ti foil caused the Mo rod and tube at the interface to melt. The melted Mo and Ti together formed an MBZ. The Mo in the MMZ 300-800 μm away from the WB came only from interfacial melting. Thus, this zone is defined as the ...
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... in both zones, which was a result of the significant difference in melting points between Mo and Ti and the high thermal conductivity of Mo. Finally, the mechanism of formation of the MBZ N 1200 μm away from the WB is analysed. During the welding process, the maximum temperature in this zone was lower than the melting point of Ti (P D curve in Fig. 11(b)). The Mo at the interface was thus unable to enter this zone by melting. However, this zone had a temperature exceeding 1100 °C, the lowest temperature for effective Mo\ \Ti diffusion [42,43]. Thus, there was a 5-μm-wide Mo\ \Ti transitional distribution zone (diffusion zone (DZ)) at the interface (Fig. 11(e) and (h)). Because Mo is ...
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... the melting point of Ti (P D curve in Fig. 11(b)). The Mo at the interface was thus unable to enter this zone by melting. However, this zone had a temperature exceeding 1100 °C, the lowest temperature for effective Mo\ \Ti diffusion [42,43]. Thus, there was a 5-μm-wide Mo\ \Ti transitional distribution zone (diffusion zone (DZ)) at the interface (Fig. 11(e) and (h)). Because Mo is prone to diffusion in Ti [42,43,48], the DZ was closer to the Ti foil side. The presence of the DZ indicates metallurgical bonding at the interface of this zone. However, the metallurgical bonding interface within this zone was relatively few and consequently did not significantly improve the strength (Fig. ...
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... interface (Fig. 11(e) and (h)). Because Mo is prone to diffusion in Ti [42,43,48], the DZ was closer to the Ti foil side. The presence of the DZ indicates metallurgical bonding at the interface of this zone. However, the metallurgical bonding interface within this zone was relatively few and consequently did not significantly improve the strength (Fig. ...
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... bonding at the Mo tube-Mo rod interface in the HAZ of the joint resulted in an increase in its bearing area, which in turn resulted in the migration of the stress concentration site at the Mo tubeMo rod interface from the weak boundary of the weld bead zone (I) to the relatively strong base material zone (II), as shown in Fig. 13 (c) and (d). Consequently, fracture occurred to the base material of the Mo tube during the tensile test (Fig. 7(a) and ...
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... layer on the Mo grain-boundary surface, thereby reducing the grain-boundary strength [20]. Considering the deficiencies in the above mentioned elements and based on the selection criteria for alloying elements introduced in the previous paragraph, Ti is found to have notable advantages. First, no brittle phase is formed when mixing Ti and Mo (Fig. 1); Ti and Mo are infinitely miscible in one another at high temperatures. Second, Ti can easily combine with O [15,21], thereby reducing the content of free O in Mo. Moreover, because the solidification temperature of Ti (1670 °C [22]) is far lower than that of Mo (2623 °C [22]), Ti is prone to crystallize at the Mo grain boundaries and ...
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... are explained from phase transition and energy perspectives. First, the O in the base metal and shielding gas could enter the welding pool during the welding process as the impurity element. In addition, the melted Ti foil is evenly distributed in the welded zone as a result of the stirring action of the welding pool (Fig. 3 (b); S1, S2 and S3 in Fig. 10). Owing to its low melting point (1670 °C), Ti is transported to the Mo grain boundaries during the crystallization process [23]. Considering the high cooling rate (200-500 K·s −1 ) of the welding pool, some Ti could form a solid solution inside the Mo grains [42,43], and the majority of the O is precipitated at the Mo grain boundaries ...
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... Owing to its low melting point (1670 °C), Ti is transported to the Mo grain boundaries during the crystallization process [23]. Considering the high cooling rate (200-500 K·s −1 ) of the welding pool, some Ti could form a solid solution inside the Mo grains [42,43], and the majority of the O is precipitated at the Mo grain boundaries [5,7] (S4 in Fig. 10). As the temperature of the welding pool decreases to approximately 2300 ± 150 °C, the MoO 2 phase could be firstly precipitated at the Mo grain boundaries (S5 in Fig. 10). When the temperature drops to 1870 °C (the solidification point of TiO 2 [22]), the Ti solid solution in the Mo grains combines with O, forming TiO 2 [15,21,22]; in ...
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... K·s −1 ) of the welding pool, some Ti could form a solid solution inside the Mo grains [42,43], and the majority of the O is precipitated at the Mo grain boundaries [5,7] (S4 in Fig. 10). As the temperature of the welding pool decreases to approximately 2300 ± 150 °C, the MoO 2 phase could be firstly precipitated at the Mo grain boundaries (S5 in Fig. 10). When the temperature drops to 1870 °C (the solidification point of TiO 2 [22]), the Ti solid solution in the Mo grains combines with O, forming TiO 2 [15,21,22]; in addition, the Ti precipitated at the Mo grain boundaries combines with O, forming TiO 2 , and some surplus Ti at the Mo grain boundaries could cause the reduction of some ...
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... °C (the solidification point of TiO 2 [22]), the Ti solid solution in the Mo grains combines with O, forming TiO 2 [15,21,22]; in addition, the Ti precipitated at the Mo grain boundaries combines with O, forming TiO 2 , and some surplus Ti at the Mo grain boundaries could cause the reduction of some MoO 2 at the Mo grain boundaries [44] (S6 in Fig. 10), thereby reducing the MoO 2 content at the Mo grain boundaries. Eq. (1) shows this reduction reaction. At a temperature lower than 1870 °C, the free energy of this reduction reaction is b0 (eq. (2), eq. (3) [46], eq. (4) [46], eq. (5) [44], eq. (6) [44]) and, from a thermodynamic perspective, can take place spontaneously [45]. Table 4 ...
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... tensile strength of the Mo-0.03Ti-B joint alloying by method B was the same as that of the base material (Fig. 7(a)). The backscattered electron (BSE) image of the cross-section of the Mo-0.03Ti-B joint (Fig. 11(a)) shows that a metallurgical bonding zone (MBZ) was formed at the location where the Ti foil was pre-placed in the HAZ. The composition of the MBZ exhibited a notable gradient variation in the axial direction (AD) of the Mo tube. The thickness of the MBZ, which is within 800 μm of the welded zone, was greater than the original thickness ...
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... Mo 38.103wt%-Ti 61.658wt%, respectively. In other words, the farther away from the weld bead, the higher content of Ti was in the MBZ. The EDS line-scanning of sites B and C in the MBZ ≤ 800 μm away from the WB also show that Mo and Ti were evenly distributed along the whole metallurgical bonding interface in the radial direction of the Mo tube (Fig. 11(c) and (d)). The MBZ ≤ 800 μm away from the WB was composed of a mixture of Mo and Ti and N30 μm in thickness, and hence is defined as a mixed melting zone (MMZ). The middle layer, which is 1200 μm away from the welded zone, contained 99.901 wt% Ti and was as thick as the original Ti foil. Thus, this zone was the original Ti foil ...
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... the mechanism of formation of the MMZ is analysed. The MMZ contained a high Mo content, which gradually decreased as the distance in the AD from the fusion zone increased (Fig. 11(a)). Mo had two possible sources: (1) the melting of the Mo rod and tube on the two sides of the interface of the MMZ and (2) the Mo contained in the welding ...
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... sources of Mo in the MMZ were analysed using the zirconium (Zr) tracing method, as shown in Fig. 12(a). The results show that the WB and the MBZ ≤300 μm away from the welded zone both contained significant amounts of Zr after welding (Fig. 12(c)), suggesting that the Mo in the MBZ ≤ 300 μm away from the WB came partially from the welding pool. In addition, the thickness of the MBZ ≤ 300 μm away from the WB ranged from 60 to 50 μm, ...
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... sources of Mo in the MMZ were analysed using the zirconium (Zr) tracing method, as shown in Fig. 12(a). The results show that the WB and the MBZ ≤300 μm away from the welded zone both contained significant amounts of Zr after welding (Fig. 12(c)), suggesting that the Mo in the MBZ ≤ 300 μm away from the WB came partially from the welding pool. In addition, the thickness of the MBZ ≤ 300 μm away from the WB ranged from 60 to 50 μm, significantly greater than that of the Ti foil (30 μm), indicating that the Mo rod and tube on the two sides of the interface also melted. The ANSYS ...
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... μm away from the WB ranged from 60 to 50 μm, significantly greater than that of the Ti foil (30 μm), indicating that the Mo rod and tube on the two sides of the interface also melted. The ANSYS simulation results for the temperature field during the welding process show that the maximum temperature at site B (250 μm away from the welded zone) in Fig. 11 (a) ranged from 1670 to 2623 °C, and the Ti foil could be melted with this temperature range. In addition, based on the infinite mutual miscibility of Mo and Ti, shown in the phase diagram in Fig. 1, a large amount of Mo at the Mo rod-Mo tube interface melted and entered the liquid Ti [47]. Thus, the Mo in the MMZ 0-300 μm away from ...
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... results for the temperature field during the welding process show that the maximum temperature at site B (250 μm away from the welded zone) in Fig. 11 (a) ranged from 1670 to 2623 °C, and the Ti foil could be melted with this temperature range. In addition, based on the infinite mutual miscibility of Mo and Ti, shown in the phase diagram in Fig. 1, a large amount of Mo at the Mo rod-Mo tube interface melted and entered the liquid Ti [47]. Thus, the Mo in the MMZ 0-300 μm away from the WB came partially from the Mo rod and tube melted at the interface and partially from the welding ...
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... metals in the welding pool were unable to enter the zone 300-800 μm away from the WB. However, the Mo content at points 3 and 4 in Fig. 11(a) was as high as 54.554 wt% and 38.106 wt%, respectively. Theoretically, Mo could only come from the melted base material on the two sides of the interface. The ANSYS simulation results show that the maximum temperature at site C (Fig. 11(a)), which was 700 μm away from the WB, was N1670 °C, meeting the condition for the melting of the ...
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... pool were unable to enter the zone 300-800 μm away from the WB. However, the Mo content at points 3 and 4 in Fig. 11(a) was as high as 54.554 wt% and 38.106 wt%, respectively. Theoretically, Mo could only come from the melted base material on the two sides of the interface. The ANSYS simulation results show that the maximum temperature at site C (Fig. 11(a)), which was 700 μm away from the WB, was N1670 °C, meeting the condition for the melting of the Ti foil. The melted Ti foil caused the Mo rod and tube at the interface to melt. The melted Mo and Ti together formed an MBZ. The Mo in the MMZ 300-800 μm away from the WB came only from interfacial melting. Thus, this zone is defined as the ...
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... in both zones, which was a result of the significant difference in melting points between Mo and Ti and the high thermal conductivity of Mo. Finally, the mechanism of formation of the MBZ N 1200 μm away from the WB is analysed. During the welding process, the maximum temperature in this zone was lower than the melting point of Ti (P D curve in Fig. 11(b)). The Mo at the interface was thus unable to enter this zone by melting. However, this zone had a temperature exceeding 1100 °C, the lowest temperature for effective Mo\ \Ti diffusion [42,43]. Thus, there was a 5-μm-wide Mo\ \Ti transitional distribution zone (diffusion zone (DZ)) at the interface (Fig. 11(e) and (h)). Because Mo is ...
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... the melting point of Ti (P D curve in Fig. 11(b)). The Mo at the interface was thus unable to enter this zone by melting. However, this zone had a temperature exceeding 1100 °C, the lowest temperature for effective Mo\ \Ti diffusion [42,43]. Thus, there was a 5-μm-wide Mo\ \Ti transitional distribution zone (diffusion zone (DZ)) at the interface (Fig. 11(e) and (h)). Because Mo is prone to diffusion in Ti [42,43,48], the DZ was closer to the Ti foil side. The presence of the DZ indicates metallurgical bonding at the interface of this zone. However, the metallurgical bonding interface within this zone was relatively few and consequently did not significantly improve the strength (Fig. ...
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... interface (Fig. 11(e) and (h)). Because Mo is prone to diffusion in Ti [42,43,48], the DZ was closer to the Ti foil side. The presence of the DZ indicates metallurgical bonding at the interface of this zone. However, the metallurgical bonding interface within this zone was relatively few and consequently did not significantly improve the strength (Fig. ...
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... bonding at the Mo tube-Mo rod interface in the HAZ of the joint resulted in an increase in its bearing area, which in turn resulted in the migration of the stress concentration site at the Mo tubeMo rod interface from the weak boundary of the weld bead zone (I) to the relatively strong base material zone (II), as shown in Fig. 13 (c) and (d). Consequently, fracture occurred to the base material of the Mo tube during the tensile test (Fig. 7(a) and ...
Citations
... As a result of these factors, the strength of Mo welded joint is generally only 30-50% of that of the base material [18][19][20][21][22][23]. Zhang et al. [24] investigated influences of titanium (Ti) alloying in the fusion zone (FZ) and Ti alloying in the heat affected zone (HAZ) on the microstructures and performance of socket joints of Mo alloys. The room-temperature tensile strength of the obtained socket joints reaches 94.9% of the strength of the BM of Mo tubes. ...
... As shown in Fig. 1(c), the Ti foil was also placed in the HAZ of the LW-Ti-B joints. Zhang et al. [24] found that some Ti on the overlapping interface in the HAZ entered the FZ in the welding process. The surface tension of the molten Ti is 1410 mN⋅m − 1 (below 1668 • C), whereas that of molten Mo is 2250 mN⋅m − 1 (below 2620 • C) [33]. ...
... The line scanning results along Path 3 in the figure show that the metals in the brazing zone near the FZ were a mixture of Mo and Ti, and the mixed zone of the two elements was approximately 1 mm wide. As the distance to the FZ boundary gradually increased, the Mo content in the mixed zone of the two elements gradually decreased, and the Ti content gradually increased [24]. ...
Three types of Mo alloy socket joints were prepared in this study: a joint without alloying (LW joint), a joint with a trace amount of titanium (Ti) added to the fusion zone (FZ) (LW-Ti-A joint), and a joint with Ti separately added to the FZ and the heat affected zone (HAZ) (LW-Ti-B joint). Tensile tests were carried out on the three types of joints at 360, 900, and 1200 ◦ C. The results showed that the tensile strengths of the base metal (BM) of the Mo tubes were 368.7, 239.9, and 189.6 MPa at 360, 900, and 1200 ◦ C, respectively. At all temperatures, the tensile strengths of the welded joints increased in the order of LW, LW-Ti-A, and LW-Ti-B, which indicates that adding Ti to the FZ and HAZ separately had an obvious strengthening effect. The fracture positions of the joints were primarily affected by the Ti alloying scheme. The LW joints are always fractured at the FZ, showing brittle intergranular fractures; the LW-Ti-A joints fractured at the BM or the HAZ near the FZ; and the LW-Ti-B joints fractured at the BM far from the FZ, exhibiting ductile fracture. Adding Ti to the FZ can induced a solid-solution strengthening effect, which refined the grain size in the FZ by approximately 30–40% and reduced the amount of Mo oxide on the grain boundaries in the FZ, thus improving the joint strength. Presetting a Ti foil on the overlapping interface in the HAZ realized metallurgical bonding between the Mo tube and Mo end plug in the HAZ of the laser-welded joints, enlarge the bearing area, and improve the joint strength. And a new metallurgical bond zone is formed on the overlapping interface in the HAZ during the high-temperature tensile tests of the welded joints, which further improve the joint strength.
... Higher magnification micrograph, as seen in Fig. 8b, indicated the presence of a large number of irregular oxide particles at most of the grain boundaries in the sample. Liang-Liang Zhang et al. [62] reported similar observations of oxide particles at fracture surfaces in laser welding of Mo. Mallett [63] observed that with increasing oxygen content, the shape of precipitates at the grain boundaries changes from discrete precipitates to continuous film. ...
... Also, the high Mo content in the weld-metal zone improves creep resistance, thereby reducing the dislocations that occur at high temperatures. [41,42]. ...
ASTM Mar-M247 is one of the superalloys used to manufacture gas turbine blades in power stations. This paper studies the microstructure across welded joints of a turbine blade made of a high-strength material (Mar-M247 alloy) employing AWS ERNiCrMo-3 as a filler alloy. This process was carried out using gas tungsten arc welding (GTAW). The dendritic and interdendritic structures were observed in the fusion zone. The results also showed the presence of epitaxial growth at the interface between the weld metal and the base alloy without solidification cracks. Al and Co concentrations gradually decrease towards the weld metal zone during the solidification process, while Cr content increases towards the fusion zone. Vickers hardness revealed that the hardness in the heat-affected zone (HAZ) is higher than that of the base metal and the weld metal zone, the average in the HAZ is 340HV, while in the base metal and the fusion zone is 322HV, 284HV respectively. Coarse grains in the HAZ were found with an agglomeration of carbides at the grain boundaries due to the input heat of the welding process.
Keywords
Gas turbine blade; Mar-M247; GTAW; Filler alloy; Microstructure; Hardness
... Based on the literature [23], the increase in Mo content increases the Fig. 1. Binary Mo-Ti alloy phase diagram [26]. Redrawn with permission from Elsevier. ...
... It can be seen from MoeTi binary-phase diagram that Mo and Ti can form infinite sosoloids while do not produce brittle phases, so Ti is an ideal microalloying element. Zhang et al. [20] found that adding Ti to the weld of Mo can inhibit generation of precipitates with low properties on grain boundaries and significantly improve the strength of grain boundaries. According to the ReeTi binary-phase diagram, the solid solubility of Re in Ti can reach 45 at% Re, indicative of high metallurgy compatibility of Re and Ti. ...
... According to the ReeTi binary-phase diagram, the solid solubility of Re in Ti can reach 45 at% Re, indicative of high metallurgy compatibility of Re and Ti. Moreover, Zhang et al. [20] proposed a processing method to form a brazing zone in the HAZ of joints based on the great disparity of Mo and Ti in the boiling point, high thermal conductivity of Mo alloys, and structural characteristics of socket joints. The method significantly improves the tensile strength of joints and provides a favorable reference for fusion welding of socket joints of refractory materials. ...
Fusion welding of molybdenum (Mo) alloys faces problems including grain coarsening and embrittlement, so that the obtained joints have poor mechanical performance. The research took the socket joints of a novel Mo-14Re ultra-high-temperature (UHT) heat pipe as research objects. Pre-heating, titanium (Ti) microalloying and brazing were adopted for coordinated regulation of defects, microstructures, and mechanical performance of joints. Results show that Ti added can be uniformly mixed with metals in the molten pool and solidly dissolved in the matrix to achieve solid-solution strengthening. Ti entering the weld zone distributes on grain boundaries and in grains, thus decreasing the relative content of Mo oxides on the surface of grain boundaries in the meanwhile of grain refinement, playing a role in purifying grain boundaries. Ti alloying in the weld zone to some extent can inhibit occurrence of pore defects and improve the bearing capacity of joints. Moreover, the brazing layer formed in the heat affected zone (HAZ) not only enlarges the bonding and bearing area of joints, but also shifts the position of the stress concentration point of joints from the near weld zone with poor performance to the area with favorable performance much farther from the weld. Under the joint action of Ti microalloying and brazing, the tensile strength of joints is improved from 140.8 to 399.8 MPa. The fracture mode changes from intergranular fracture to transgranular cleavage-like fracture. The research results can promote the development of technologies for manufacturing novel UHT heat pipes and welding Mo-Re alloys.
... They analyzed the flow of material in the molten pool encirclement the keyhole to discover the flow of vortex in the molten pool beyond the keyhole by inserting a tungsten particle in the base metal. Previous researchers have addressed the potential to reduce laser welding pressure by increasing the laser energy [12], [13]. Other attempts on welding a stainless steel material by controlling the power laser to about 26 kilowatts attained a reasonable quality welding of 75 millimeter of penetrationdepth with one meter per minute speed single-pass laser beam welding at one kilo Pascal pressure [14], [15]. ...
The process of remote laser welding is simulated in this study to identify the keyhole-induced porosity generation mechanisms and keyhole. Three processes are simulated and discussed: laser power levels, laser-beam shaping configurations, and laser keyhole process. The simulation finding reveals that pore development is caused by strong melt flow behind the keyhole. As verification, the equivalent experimental test is also carried out. According to the findings, a welding speed with a high level helps to keep the keyholes released and prevents the flow of strong melt; a big advanced leaning-angle also provides inactive molten pool flow, making it difficult for bubbles to float to the backside of the molten pool. The conclusions of this study offer crucial insight into the method of porosity of aluminum (Al) alloys laser welding, as well as advice on how to avoid keyhole-induced porosity. It is also obtained that a smaller laser beam with constant power raises the velocity, welding pool depth, and liquid metal temperature. Keywords: Computational fluid dynamics simulation Fluid flow analysis Heat transfer Laser-based welding Solidification This is an open access article under the CC BY-SA license.
... They analyzed the flow of material in the molten pool encirclement the keyhole to discover the flow of vortex in the molten pool beyond the keyhole by inserting a tungsten particle in the base metal. Previous researchers have addressed the potential to reduce laser welding pressure by increasing the laser energy [12], [13]. Other attempts on welding a stainless steel material by controlling the power laser to about 26 kilowatts attained a reasonable quality welding of 75 millimeter of penetrationdepth with one meter per minute speed single-pass laser beam welding at one kilo Pascal pressure [14], [15]. ...
The process of remote laser welding is simulated in this study to identify the keyhole-induced porosity generation mechanisms and keyhole. Three processes are simulated and discussed: laser power levels, laser-beam shaping configurations, and laser keyhole process. The simulation finding reveals that pore development is caused by strong melt flow behind the keyhole. As verification, the equivalent experimental test is also carried out. According to the findings, a welding speed with a high level helps to keep the keyholes released and prevents the flow of strong melt; a big advanced leaning-angle also provides inactive molten pool flow, making it difficult for bubbles to float to the backside of the molten pool. The conclusions of this study offer crucial insight into the method of porosity of aluminum (Al) alloys laser welding, as well as advice on how to avoid keyhole-induced porosity. It is also obtained that a smaller laser beam with constant power raises the velocity, welding pool depth, and liquid metal temperature.
... Alloying zirconium also has a beneficial effect on welded joints because the gettering of oxygen leads to purification of the grain boundaries [7,8,13]. Similarly, minor additions of titanium led to the formation of TiO2, which reduced the amount of pure oxygen and MoO2 at the grain boundaries [14]. Pre-nitriding of the base metal or laser gas (N2) alloying can enhance the mechanical properties of Mo joints due to the strengthening effect of Mo2N [15,16]. ...
Joining molybdenum-based materials by fusion welding causes a deterioration of mechanical properties due to local alterations of the microstructure. Sheets of pure molybdenum (Mo), as well as boron doped Mo (MoB15) and TZM were welded with the same process parameters to investigate the correlations between alloy composition and the process-induced changes in microstructure and mechanical properties. Furthermore, the impact of the laser power distribution and heat treatment after welding was investigated. For this purpose, room temperature tensile tests were carried out. The fracture surfaces were analyzed to determine the fracture mechanisms. The crack paths were investigated by means of microsections of the tested tensile specimens. The results show that intergranular fracture in the middle of the fusion zone is the overall most occurring failure. Recrystallization after laser welding can cause a shift towards cracks along the fusion line in Mo and into the base metal in TZM. MoB15 often exhibits transgranular cracks within the fusion zone, regardless of the heat treatment. The laser power distribution had no significant impact on the component properties.
... La mauvaise soudabilité du Mo s'explique d'une manière générale par la présence d'oxydes MoO 2 fragilisant les joints de grains. Le Ti a une meilleure affinité avec l'oxygène et permet par conséquent de remplacer MoO 2 par TiO 2 moins gênant [134], permettant à la zone fondue d'être plus résistante. ...
La réalisation des assemblages dissimilaires par laser entre les nuances de titane et d’acier inoxydable représente un grand intérêt pour différentes applications industrielles. Cependant, un assemblage direct par fusion de ces matériaux est difficilement réalisable à cause de l’existence de phases intermétalliques fragiles dans le système Ti-Fe provoquant la fissuration spontanée des jonctions. L’objectif scientifique de cette thèse est de déterminer un critère fiable permettant d'identifier, si elles existent, les conditions d'obtention d'une jonction bimétallique titane/inox durable, en termes de tenue mécanique en service des assemblages. La détermination de ce critère est nécessaire pour la compréhension du lien entre la microstructure d'un joint soudé et la tenue mécanique de la structure soudée. Un autre objectif est de prouver la faisabilité de l'assemblage titane/inox par soudage laser dans le contexte particulier d'une production industrielle de petite série de pièces.Pour répondre à cette problématique, dans un premier temps, la faisabilité des assemblages directs, sans matériau d’apport, a été étudiée. L'application d'un décalage extrême du faisceau laser sur le titane a permis de réduire le développement des phases fragiles à une interface réactionnelle micrométrique située à la limite de la zone fondue, et de cette manière d'obtenir des assemblages sans défauts apparents. Cependant, ces assemblages montrent un comportement fragile en traction avec des coefficients de joint faibles et une nature probabiliste de la propagation de la rupture.L’utilisation d'inserts de matériaux ayant une compatibilité métallurgique idéale avec le titane (le vanadium et le niobium) en configuration bipasse avec deux zones fondues isolées, a permis de s’affranchir de la fragilisation liée aux phases intermétalliques se formant entre l’inox et le titane. Les assemblages réalisés avec un insert vanadium ont montré un coefficient de joint élevé et un comportement ductile en traction dans une plage suffisamment large des paramètres opératoires, alors que les assemblages réalisés avec un insert en niobium ont montré des performances équivalentes aux assemblages réalisés sans insert à cause de la formation de phases fragiles dans la zone fondue niobium/inox.Finalement, une approche multi-inserts avec un soudage en trois passes d’un assemblage titane/niobium/cuivre/inox a été testée. Une absence de phases intermétalliques dans les systèmes binaires pris à part a permis d'obtenir un comportement ductile à la traction et une résistance mécanique limitée par celle de l’insert en cuivre.Ce travail a permis d’identifier les solutions concrètes permettant de répondre aux besoins industriels de production des assemblages dissimilaires titane-inox en petite série, et mis en lumière les difficultés de production liées à la reproductibilité des microstructures et à la qualité de la préparation des pièces à assembler.
... For example, Noda et al. [7] obtained some samples with different O content by controlling the heating time in an oxygen atmosphere and measured the O content at the grain boundary surface by AES. His results showed that reducing the O content at the grain boundary could significantly improve the strength and ductile -brittle transition temperature; Zhang et al. [8,9] found Ti, Zr added in the fusion zone of laser welding joint of Mo could react with O and the content of O was decreased by adding active elements. The grain boundary is also strengthened by adding the second phases or second phase forming elements. ...
... Zhang et al. [9] found the Zr added in the FZ of joints could reacted with O to form ZrO 2 then decreasing the content of O. And Ti added into the FZ of joints could reacted with O to form TiO 2 then decreasing the content of O [8]. ...
Molybdenum (Mo) is of great potential in the nuclear energy field, however, the embrittlement and the lower tensile strength limit the application of the fusion welded joints. Titanium (Ti) and zirconium (Zr) were synchronously added into the fusion zone (FZ) to improve the tensile strength and certain ductility of laser beam welding joints. By utilizing high-resolution scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and nanoindentation, the microstructures and mechanical properties of FZs in the joints under different alloying strategies with Ti and Zr were analyzed. Zr is mainly present in Mo as Mo2Zr, playing the second-phase strengthening effect; Ti is mainly present in Mo in an atomic state, playing a role of the solid - solution strengthening. The addition of Ti and Zr with different mass proportions can control the relative contents of Mo2Zr phase and solid - solution atoms in the FZ, control the distribution of zigzag and flat grain boundaries and influence the relative distributions of low - angle grain boundaries (LAGBs) and high - angle grain boundaries (HAGBs). In the end, combined addition of Ti and Zr is possible to improve the tensile strength while decrease the loss of ductility of the joint.
