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首页> 外文期刊>Materials Science and Engineering >Site-specific microstructure, porosity and mechanical properties of LENS™ processed Ti-6Al-4V alloy
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Site-specific microstructure, porosity and mechanical properties of LENS™ processed Ti-6Al-4V alloy

机译：特异性微观结构，孔隙率和机械性能的镜片™加工Ti-6Al-4V合金

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摘要

In the present study, pre-alloyed Ti-6Al-4V powder is deposited on CP-Titanium substrate by laser engineered net shaping (LENS™) process using parameters optimized for best adhesion and densification. The optical montages from the three surfaces (front, side and top) show columnar β grains growing along the building direction due to conductive heat transfer through the substrate. The as-deposited microstructure contains thin lamellar (α+β)-colonies besides prior β grain boundaries and basket-weave (α+β)-structure inside prior β grains. Narrow band-like structure forms between consecutive layers due to re-melting of previously deposited layers, thereby creating additional interfaces in the microstructure. In addition, tiny isolated pores appears in negligible fraction throughout the LENS™-processed specimen due to gas entrapment, shrinkage during cooling and un-melted or partially melted powder particles. Both the number and volume of the pores increase along the building direction. Hardness on different surfaces (front, side and top) differs considerably due to the presence of different heating/cooling zones, residual stresses and variations in the thermal cycles and consequent change in the α -martensite phase fraction. Larger variation in the hardness between these surfaces is observed in nano-indentation technique signifying for inhomogeneity in nano-scale structure. These microstructural variations also resulted in measurable changes in the coefficient in friction (COF) during scratch testing from the substrate along the building direction due to presence of different heating/cooling zones (diffused vs. reheating/re-melting zones). The variation in hardness and COF along different directions can ultimately lessen the in-service performance of the as-deposited parts.
机译：在本研究中，使用针对最佳粘合和致密化的参数，通过激光工程网整形（LENED™）工艺在CP钛基板上沉积预合金的Ti-6Al-4V粉末。来自三个表面（前，侧和顶部）的光学蒙太孔显示由于通过基板的导电热传递而沿建筑方向生长的柱状β颗粒。除了先前β晶界和篮织物（α+β） - 在现有β颗粒中，沉积的微观结构含有薄的层状薄层（α+β）灰度。由于先前沉积层的重新熔化，连续层之间形成窄带结构，从而在微结构中产生附加接口。此外，由于气体截留，微小的分离孔隙在整个透镜™的渗透标本中出现可忽略的分数，冷却和未熔化或部分熔化的粉末颗粒期间的收缩。孔的数量和体积沿建筑方向增加。由于存在不同的加热/冷却区域，残余应力和热循环中的变化以及α-淀粉沸石相位级分的发生变化，不同表面上的硬度不同。在纳米尺度结构中的纳米缩进技术中观察到这些表面之间的硬度变化的变化。由于存在不同的加热/冷却区域（扩散与再加热/再熔断区），这些微观结构变化也导致沿着基板的划痕测试过程中的摩擦系数（COF）的变化。沿不同方向的硬度和COF的变化最终可以减少沉积部件的适用性性能。

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