Sduty On Property And Stability Of Organization Of Ni/Ni₃Si Composite Alloy

High temperature Intermetallic compounds possess many attractive properties for potential high temperature applications.Eespecialy,Ni-Si system high temperature intermetallies is valued for excellent performance such as good corrosion resistance, oxidation resistance, high elastic modulus, high electrical conductivity, thermal conductivity, relatively low density and exceptional strength-temperature (or R characteristic).It is used broadly not only in aviation and aerospace fields,but also as important materials in transportation,chemaical,machinary and other industries sector.However,like other high-temperature metal silicide alloys, the higher brittleness at room temperature and lower strength at high temperature of the Ni-Si system has been the focus of attention.This paper is based on the principles of complex modification,the Ni powder and Si powder as raw materials, alloy materials were prepared by arc melting with different Si content. At the same time,Various methods such as XRD, OM, SEM and EDS and other methods were used to do the phase analysis,microstructure observation and micro-component analysis.We systematically analyze the microstructure and properties of the samples that has different Si components and do systematically research in the thermal stability of the test samples.the following observations are obtained:(1)Phase analysis of specimens with the different Si compontents indicating the main phase of the Ni-Si alloy samples are Ni₃Si,Ni.There are Ni₃₁Si₁₂ and Ni₇₄Si₂₆ in the alloy samples with different Si content.Ni₃₁Si₁₂å’ŒNi₇₄Si₂₆ are metastable phases.it can be eliminated by high temperature annealing. Eutectic alloy have lamellar organizations and part of the eutectic region has very regular structure of lath.(2)There is a significant upward trend in hardness of the alloy samples with different Si content.The values of the hardness is between the 495HV and 673HV. Flexural strength and compressive strength increased with different Si content was first increased and then decreased. Ni phase precipitation help to improve the fracture toughness. It reached the peak when the Si content of the samples is at 21.41 (at.%). The values of eutectic in flexural strength and compressive strength and hardness are in the middle.We can see that there are no cracks in the indentation under the weight of 50 kg.The results indicate that Ni-Si eutectic alloy is better overall performance.(3)We insulated our samples in different temperatures for different time.We found that the eutectic alloy phases of the samples insulated in 900 for 30h are Ni₃Si phase and Ni phase.The range of the grain size is narrow,the size of the sheet remains the same and the organization is relatively stable.At 1000℃and 1100℃,the oxidation of eutectic alloy has started.With the extension of the insulate time,the Ni3Si superstructure peak has vanished, the organization become extremely unstable.By the contrasts of the eutectic alloy in three different temperatures and three different time,we found that the alloy laminar size increases gradually and the region spheroidizes, the laminar quantity reduced along with temperature increase. The sheet structure has a better stability than the non-laminar. And we also found that the micro-hardness of the eutectic alloy is between Ni and Ni₃Si, after heat preservation the values of the alloy hardness is higher than before.