Study On Selective Nitriding Process Of Cu-Si Alloy Powder

With the development of the industry, ordinary Cu alloys can’t meet the demands forhigh conductivity, high thermal conductivity and high strength. The copper basedcomposites which strengthened by the dispersion of the second phase particle not only havehigh strength, high electrical conductivity and thermal conductivity of which is close to purecopper, but also have good resistance to erosion and wear resistance. It is a new type ofmaterial that has a broad application prospect. This paper aims to study the method ofselective nitriding of Cu-Si alloy to prepare Si3N4/Cu composite material. At first, the Cu-Sialloy powder was prepared by the method of water atomization process, then thethermodynamics and kinetics of selective nitriding process of Cu-Si alloy were studied. Thenitriding process was carried on under condition of high temperature, and then controllingnitriding process parameters to find the best process parameter. This topic is focused on theinfluence of nitriding temperature and nitriding time on the nitriding rate and themorphology of powder. After that the powder which is treated under different nitridingprocess were sintered with optimized sintering parameter in SPS. Then the effects ofdifferent parameters on the hardness, electrical conductivity and microstructure of materialswere studied.The partial pressure of oxygen need to be controlled during the process of selectivenitridation, so95%N2+5%H2is adopted to be nitriding medium. During the process,temperature is the main control parameters of nitriding time with no variation of the particleradius R and the concentration of Si. Results show that nitrogen content of powder riseswith the increase of nitriding temperature and extension of nitriding time. The nitrogencontent significantly increases after separately nitriding for60h and90h in1000℃;Diffraction peaks of Cu overall apparently move to big angle, and the lattice constantdecreases at the same time, which suggests that Si exsolution from Cu based to forms Si3N4while reacts with N; The selective nitriding product and its crystalline structure have beeninvestigated with extraction method, the reinforcement in the composites is mainly-Si3N4.With nitriding temperature and time increasing, the electrical conductivity and hardnessgradually increase, but too long nitriding time will not obviously improve the hardness ofthe material. In this paper, the density of samples nitriding for90h on1000℃is99.49%,compared with the sintered specimen prepared with original alloy powder, the conductivity increased by2.94times, and the hardness reaches82.5HV, while the softening resistantability of the composites also increases at high temperature. But as a result of low nitrogenrate, while high nitriding temperature and long nitriding time will lead to decrease of thestrength and hardness of the material, In the future, more efficient nitriding method will beadopted to increase the nitrogen rate.