三元Cu_(60)Ni_(20)Cr_(20)合金的制备及其显微组织

Preparation and microstructures of Cu_(60)Ni_(20)Cr_(20) alloys

采用机械合金化,随后在750℃、58MPa下热压制备了致密的块体纳米晶Cu60Ni20Cr20合金,用X射线衍射仪、扫描电子显微镜等分析手段对比研究了不同晶粒尺寸的Cu60Ni20Cr20合金的显微组织。结果表明:随着球磨时间的延长,由于晶粒的细化和应变的结果,衍射峰偏移并有明显的宽化产生,Cr在Cu中的固溶度明显增加,在球磨40h后,合金已由双相变成亚稳态的单相。由于机械合金化的粉末处于非平衡态,其过饱和固溶体随热压和真空退火过程的进行会慢慢分解,合金由单相变成两相,α Cu和γ Cr两相颗粒均成倍长大,但仍保持纳米级尺度。扫描电子显微镜(SEM/EDX)观察表明,合金致密度很高且显微组织均匀。讨论了晶粒细化对合金显微组织的影响。

The Cu_(60)Ni_(20)Cr_(20) bulk alloys have been prepared respectively by arc-melting and hot pressing the mechanically alloyed powders at 750 ℃ under a normal pressure 58 MPa with much different grain sizes. Their micro-structural characteristics were investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM) and (energy-)dispersive X-ray microanalysis(EDX). The results show that with the increase of ball milling time, the X-ray diffraction peaks have a deviation and broadening because of fine grain size and internal stress and the solid solubility of Cr in Cu increases evidently. When the powders were milled for 40 h, the alloyed powders have become single solid solution. Because mechanically alloyed powders are in non-equilibrium state, the solvent in a state with certain degree of super-saturation can decompose slowly, finally the alloys have become double-phase from single phase solid solution. The sizes of α-Cu and γ-Cr phase particles increased but still remained nano-size after hot pressing and annealing in vacuum. The alloy possessed excellent density and showed little oxidation by SEM/EDX analysis. The effect of grain size on alloys microstructue was discussed in detail.