Vacuum heat treatments of titanium porous structures
Vacuum heat treatments of titanium porous structures
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DOI：
10.1016/j.addma.2021.102262
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发表时间：
2021-11-01
影响因子：
11
通讯作者：
Jeffers, Jonathan R. T.
中科院分区：
文献类型：
--
作者：
Ghouse, Shaaz;Oosterbeek, Reece N.;Jeffers, Jonathan R. T.
Ti-6Al-4V的增材制造（AM）可以快速制造复杂零件，包括航空航天、汽车或生物医学应用感兴趣的多孔晶格，但目前这些材料的疲劳强度是一个关键限制。设计合金微观结构提供了一种有前途的方法来增加疲劳强度，但已知常规热处理程序会产生AM和多孔样品的非典型结果，因此必须针对这些材料进行优化。使用真空热处理，显微组织相比，观察到的常规锻造和热处理合金实现与多孔AM Ti-6Al-4V。使用在920摄氏度下的亚转变热处理产生精细层状微观结构，而使用在1050摄氏度或1200摄氏度下的超转变热处理产生粗糙层状微观结构。增加热处理温度使弹性模量从2552 +/- 22 MPa增加到最大2968 +/- 45 MPa，这是由于支柱烧结增加了有效支柱厚度，并且去除了先前的13晶粒取向。热处理消除了脆性α '马氏体相，有利于α + 13混合物，其中相边界和13相提供更大的抗裂纹扩展性。超相变热处理增加了α-板条尺寸，这通常会降低裂纹扩展阻力，然而，支柱烧结减少了表面裂纹萌生部位，使疲劳强度增加了75%，从预制材料的4.86 MPa增加到1200 ℃热处理后的最大值8.51 MPa。这项工作表明，真空热处理是有效的调整微观和宏观结构的多孔AM Ti-6Al-4V，从而提高了关键的抗疲劳性。
Additive manufacturing (AM) of Ti-6Al-4V enables rapid fabrication of complex parts, including porous lattices which are of interest for aerospace, automotive, or biomedical applications, however currently the fatigue resistance of these materials is a critical limitation. Engineering the alloy microstructure provides a promising method for increasing fatigue strength, but conventional heat treatment procedures are known to produce atypical results for AM and porous samples, and must therefore be optimised for these materials. Using vacuum heat treatment, microstructures comparable to those observed for conventional wrought and heat treated alloys were achieved with porous AM Ti-6Al-4V. Fine lamellar microstructures were produced using sub-transus heat treatment at 920 degrees C, while coarse lamellar microstructures were produced using super-transus heat treatment at 1050 degrees C or 1200 degrees C. Increasing the heat treatment temperature increased the elastic modulus from 2552 +/- 22 MPa to a maximum of 2968 +/- 45 MPa, due to strut sintering increasing the effective strut thickness, and removal of prior 13-grain orientation. Heat treatment eliminated the brittle alpha' martensite phase in favour of an alpha + 13 mixture, where the phase boundaries and 13-phase provide greater resistance to crack propagation. Super-transus heat treatments increased the alpha-lath size which typically reduces crack propagation resistance, however strut sintering reduced surface crack initiation sites, increasing the fatigue strength by 75% from 4.86 MPa for the asbuilt material to a maximum of 8.51 MPa after 1200 degrees C heat treatment. This work demonstrates that vacuum heat treatment is effective at tuning the micro- and macro-structure of porous AM Ti-6Al-4V, thereby improving the crucial fatigue resistance.