Study On Simulation Of Ring Rolling, Microstructure And Properties For Powder Metallurgy Ti₂AlNb Alloy

To meet the demand of the large size ring for powder Ti₂ AlNb alloy in practical project,it is hoped that ring billet can be made by PM+HIP method, then the ring can be obtained by rolling deformation. In this paper, the ring rolling forming of powder Ti₂ AlNb alloy at high temperature was studied by the finite element analysis software of Simufact. According to the actual size of the ring and the theory research method of ring rolling, the dynamic virtual process of ring rolling was simulated. Observation of the real-time dynamic extension of ring, analysis of the simulation of rolling process and the deformation regular of two times with cumulative deformation of 60%, as well as the distribution of temperature and the strain in the process of rolling ring, were discussed thus can provide a reference for the establishment of ring rolling process. Followed that the ring was rolled, and the mechanical properties of alloy before and after deformation and heat treatment were tested. Using the material characterization method, such as optical microscope and scanning electron microscope, the effect of different deformation and heat treatments on the microstructure evolution and mechanical properties of the Ti₂ AlNb alloy was analyzed. The results showed that:In the process of ring rolling simulation, the temperature on the surface of the ring was first to drop and the temperature drop is larger, the greater the diameter, the thinner the thickness, the greater the temperature drop of the heart. The strain of the ring inside and outside surface is greater than the middle of the ring, inner surface is greater than the outer surface. With ring rolling deformation increases, the gap of deformation increased between inside, outside and the middle layer of ring. The distribution of temperature and strain is symmetry in the center of ring.After the rolling deformation of powder Ti₂ AlNb alloy, the tensile strength increased and the plastic is missing, and the brittle fracture occurs in large plastic deformation, while the performance was improved after heat treatment, the performance of powder Ti₂ AlNb alloy also could be improved by the process of mechanical deformation + heat treatment.The greater the deformation, the more the degree of hardening. The impact performance of alloy enhanced after 30% deformation, decreased after 60% deformation.The endurance properties at 650?/360 MPa of alloy increased after ring rolling deformation,the endurance properties at 650?/360 MPa of alloy with 30% deformation before and after the heat treatment lay between 60% deformation and without deformation of alloy.Vacancy and defects above the interface of B2 phase had a greater influence on the phase transition during solid solution treatment at 980 ?. The intracrystalline flaw of B2 phase had a greater influence on phase transition during solid solution treatment at 940 ?.Under the same heat treatment state, the size of lath O phase decreases along with the increase of the deformation, and the size of lump O phase first increases then decreases.At a certain solid solution temperature, the lump O phase precipitated in the tissues during the aging process, the greater the size and the more the quantity of it with the higher temperature, and the more the size of lath O phase substrate on B2 phase. At a certain aging temperature, the greater the size and the more the quantity of the lath O phase precipitation in the tissues with the lower solution temperature, at the same time, the smaller the size and the less the quantity of the lump O phase.The observation of the tensile fracture morphology showed that, the more thick lump O phase which precipitation after heat treatment had the poor coordination function with the other phases in the microstructure of alloy, more quantity of secondary lath O phase and the strengthening interaction between dislocation, which all had an adverse effect on the performance of alloy.The best heat treatment process for As-HIPed alloys was 940?/2h/AC+860?/24h/AC,for rolled alloys was 980?/2h/AC+900?/24h/AC.