烧结过程中Ni-Al金属间化合物形成的内耗

Internal friction of Ni-Al intermetallic compound formation in sintering process

Ni-Al金属间化合物是一类重要的高温结构材料,在多种领域具有明确的目标需求.粉末冶金技术是制备Ni-Al金属间化合物的一种重要选择.探索烧结过程中Ni-Al金属间化合物形成和转变过程,明确固相扩散反应发生温度和金属间化合物种类对调控烧结工艺和优化产品质量至关重要.本文采用内耗技术系统研究了Ni-Al粉末混合物压坯烧结过程的内耗行为.在内耗-温度谱上观察到一个显著内耗峰,随测量频率的增大而降低,但峰温无明显频率依赖性.同时,内耗峰随升温速率的增大向高温方向移动且峰值增加.分析认为,该峰与升温过程中金属间化合物NiAl3和Ni2Al3的形成有关,属于典型的相变内耗峰.此外,机械球磨可调控Ni-Al粉末混合物的微观结构,内耗峰随球磨时间增加向低温方向移动且峰值降低,表明固相扩散反应可在低温区域以较低速率进行.这与球磨过程中粉末颗粒的细化、粉末混合物的片层化、固溶度和表面能的提高以及缩短的原子扩散路径有关.同时也表明机械球磨可有效降低固相扩散反应起始温度进而降低烧结温度.

The Ni-Al intermetallic compounds,as important high-temperature structural materials,have clear target requirements in a number of fields.Powder metallurgy is an important candidate for preparing the Ni-Al intermetallic compounds.Clarifying the formation and transformation process of Ni-Al intermetallic compounds in sintering process and determining the solid diffusion reaction temperature and types of intermetallic compounds are greatly important for tailoring sintering process and optimizing product quality.In this paper,the internal friction behaviors of Ni-Al powder mixture compacts in the sintering process are systematically investigated by the internal friction technique.A typical internal friction peak is observed in the internal friction-temperature spectrum.The peak height decreases with the measuring frequency increasing,but the peak temperature is independent of frequency.Moreover,the internal friction peak shifts toward higher temperature and the peak height increases as the heating rate increases.It is reasonable that the internal friction peak belongs to the typical phase transformation internal friction peak which is associated with the formation of intermetallic compounds NiAl3 and Ni2Al3 in the heating process.Furthermore,the microstructure of the Ni-Al powder mixture can be tailored by mechanical ball-milling.The internal friction peak shifts toward lower temperature and the peak height decreases with the ball-milling time increasing,which indicates that the solid diffusion reaction can be activated at lower temperature with a slower reaction rate.This decrease is related to the refinement of powder particles,the lamellar formation of powder mixture,the enhancement of solid solution degree and surface energy,and the shortened atomic diffusion distance due to the mechanical ball-milling.It is also indicated that the mechanical ball-milling can effectively reduce the initial temperature of solid diffusion reaction,thus lowering sintering temperature.