此篇研究中，利用氣體霧化法製備Al0.5CoCrFeNi2Ti 高熵合金粉末，分別為(ⅰ) <10、(ⅱ) 10-60、(ⅲ) 60-120、(ⅳ) >120 μm四種尺寸。不僅如此，更進一步地將合金粉末應用於熱噴塗表面改質技術，製備出具有相可調性之塗層，並與本團隊先前研究之Al0.5CoCrFeNi2 合金粉末及噴塗層比較，探討鈦添加對粉末冶金行為及塗層性質所造成的效應。
由氣體霧化法製備的Al0.5CoCrFeNi2Ti合金粉末成份組成精確且分佈均勻，經XRD分析結果指出，其晶格結構隨著粒徑的增加，從單一的BCC結構，變成FCC+BCC的雙相結構。經研究指出合金粉末在經過退火熱處理後，在微觀結構上先是以花瓣狀組織，轉變成島嶼狀組織；在成份分佈上發現花瓣狀組織為富Al區所組成，以及Cr與Ni間相互排斥導致元素偏析的現象，而隨著退火溫度與時間的增加，有明顯的Cr-Fe與Ni-Ti析出物形成，且在母材中成核成長使整體晶粒尺寸縮小、晶粒數量增加，產生晶粒細化的效果。熱處理對晶格結構繞射峰的貢獻也將在本研究中討論，根據XRD與EBSD分析結果指出10-60 μm合金粉末的晶體結構在初始階段為BCC相，其中合金元素均勻地散布於BCC架構中，形成無序的B2相；此外，隨著熱處理能量的提升，晶體結構轉變為有序的BCC相與FCC相之雙相結構，爾後析出少量的Cr-Fe σ相與 Ni-Ti Hexagonal相。
在機械性質的表現上，由奈米壓痕法看出合金粉末經過熱處理後平均硬度由退火前的6.28 GPa上升到7.24 GPa，此乃是因為析出物的生成而形成的析出強化效果；而在塗層硬度的表現上發現到，相較於Al0.5CoCrFeNi2塗層的平均硬度HV206.6，在相同噴塗條件下Al0.5CoCrFeNi2Ti塗層硬度上升至平均HV359.62有顯著的提升，此大幅的提升則主要源自Ti的添加導致的固溶強化效果所致。

In this study, the Al0.5CoCrFeNi2Ti powders were fabricated by the gas-atomization method and sieved into four groups, which were (ⅰ) <10, (ⅱ) 10-60, (ⅲ) 60-120, (ⅳ) >120 μm, respectively. The as-atomized Al0.5CoCrFeNi2Ti powders were further applied in the thermal spraying technology to achieve the phase-adjustable coating. Effects of Ti addition on properties of Al0.5CoCrFeNi2Ti powders and their coatings were investigated by comparing with those fabricated with Ti-free Al0.5CoCrFeNi2 from our previous research.
The as-atomized powders were spherical with uniform element distribution and changeable crystal structure, which transformed from the single BCC phase to the FCC+BCC complex phase with increasing particle size. In order to investigate the phase transformation behavior, the annealing process was adopted, and several analytical methods were sequentially carried out. With the SEM EDS Mapping analysis, the Al-rich flower-like structure was first observed. Then, the segregation of Cr and Ni was found. Furthermore, the Cr-Fe and Ni-Ti precipitates were formed with the increase of annealing time. As the result of the formation of precipitates, the island-like structure and grain refinement were observed. XRD and EBSD results indicated that the crystal structure of the 10-60 μm as-atomized Al0.5CoCrFeNi2Ti powders were disordered BCC phase. After the annealing process, the disordered BCC phase was transferred into an ordered BCC phase and FCC phase. Meanwhile, the secondary phase of σ-phase and hexagonal phase was formed sequentially with annealing energy.
In order to evaluate the effects of heat treatment on mechanical properties of Al0.5CoCrFeNi2Ti powders and their coating, the nano-indentation test and micro-Vickers hardness test were adopted. As a result, it was measured that the average hardness of 10-60 μm HEA powder was improved from 6.28 GPa to 7.24 GPa after annealed due to the precipitation strengthening. Nevertheless, compared with Ti-free Al0.5CoCrFeNi2 coating, the average hardness of Al0.5CoCrFeNi2Ti coating was significantly improved from HV206.6 to HV359.62 due to the solid solution strengthening resulting from the Ti addition.

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