Laser powder bed fusion process and magnetic properties of Ni-Mn-Ga alloy
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摘要:
文中通过激光粉末床熔融(laser powder bed fusion,L-PBF)技术,结合热处理工艺优化策略,探索新型制造方案以实现功能性Ni-Mn-Ga合金及其复杂构件的可控制备. 结果表明,激光加工制造过程中产生了气孔、裂纹和未熔合等缺陷,裂纹主要源于快速凝固引起的大热应力. 在优化的工艺区间内,成功制备致密度97.5%以上的成形件,材料在环境温度为295 ~ 301 K时表现为L21有序奥氏体结构. 经均匀化、有序化和去应力退火热处理后,材料成分均匀性有所提高,相变温度区间变窄,相变特征温度的提高约为20 K,磁化强度显著提高. 热处理态材料在环境温度下表现为L21有序奥氏体和五层调制(5 M)马氏体结构的混合物相. 磁感应强度为5 T磁场下,热处理态材料在温度为300 K的饱和磁化强度可达到65.8(A·m2)/kg. L-PBF能够制备功能性 Ni-Mn-Ga磁性形状记忆合金.
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关键词:
- 激光粉末床熔融 /
- 热处理 /
- 磁性形状记忆合金 /
- Ni-Mn-Ga合金
Abstract:Laser powder bed fusion (L-PBF) technology combined with optimized heat treatment strategies was used to explore a new manufacturing scheme to achieve the controllable fabrication of functional Ni-Mn-Ga alloys and complex components. The results show that defects including porosity, cracks, and lack-of-fusion are generated during laser processing, with cracks primarily originating from significant thermal stresses induced by rapid solidification. Within the optimized process interval, parts with a density of more than 97.5% are successfully prepared, and the materials showed L21-ordered austenite structure at the ambient temperature of 295~301 K. After homogenization, ordering, and stress-relief annealing treatments, the material demonstrates improved compositional homogeneity, narrowed phase transformation temperature interval, elevated phase transition characteristic temperatures by approximately 20 K, and significantly enhanced magnetization. At ambient temperature, the material exhibits a mixed phase comprising L21-ordered austenite and five-layered modulated (5M) martensite structures. Under a magnetic field with a magnetic induction intensity of 5 T, the heat-treated material achieves a saturation magnetization of 65.8 (A·m2)/kg at 300 K. L-PBF can fabricate functional Ni-Mn-Ga magnetic shape memory alloys.
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表 1 L-PBF成形Ni-Mn-Ga合金工艺参数与致密度
Table 1 Process parameters and relative density of Ni-Mn-Ga alloy formed by L-PBF
编号 激光功率
P/W扫描速度
ν/(mm‧s−1)层厚
t/μm扫描间距
h/μm体积能量密度
ρe/(J‧mm−3)密度
ρ/(g‧cm−3)致密度
Ρr (%)1 100 1500 50 80 16.67 6.8683 86.90 2 100 2000 50 80 12.50 6.1433 77.72 3 150 1000 50 80 37.50 7.7094 97.54 4 150 1200 50 80 31.25 7.7225 97.70 5 150 1500 50 80 25.00 7.5686 95.76 6 150 2000 50 80 18.75 7.2311 91.49 7 200 1200 50 80 41.67 7.6519 96.81 8 200 2000 50 80 25.00 7.5082 94.99 9 150 1200 50 100 25.00 7.6346 96.59 10 150 1200 50 60 41.67 7.6841 97.22 表 2 热处理前后成分变化(原子分数, %)
Table 2 Compositions change before and after heat treatment
样品 数值类别 Ni元素 Mn元素 Ga元素 预合金粉末 平均值 48.38 29.88 21.74 预合金粉末 标准差 0.31 0.40 0.24 3 平均值 49.03 29.18 21.79 3 标准差 0.47 0.26 0.42 HT3 平均值 49.01 29.49 21.50 HT3 标准差 0.22 0.26 0.37 表 3 热处理前后的相变温度
Table 3 Transition temperatures before and after heat treatment
样品 测试方法 马氏体转变开始温度
Ms / K马氏体转变结束温度
Mf / K奥氏体转变开始温度
As / K奥氏体转变结束温度
Af / K居里温度
Tc / K3 DSC 258 241 261 276 369 3 VSM 264 256 265 272 368 HT3 DSC 275 265 285 297 381 HT3 VSM 282 278 284 289 377 表 4 热处理前后的相变温宽及热滞后
Table 4 Phase transformation temperature width and thermal hysteresis before and after heat treatment
样品 测试
方法马氏体转变温宽
ΔMM / K奥氏体转变温宽
ΔMA / K相变热滞后
ΔThys / K3 DSC 17 15 19.0 3 VSM 8 7 8.5 HT3 DSC 10 12 21.0 HT3 VSM 4 5 6.5 -
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