Study On Forging Properties And Optimization Of Process Of Ti40Burn Resistant Titanium Alloy

Ti40burn resistant titanium alloy is high alloying beta type titanium alloy withproprietary intellectual property rights of our country, which has good burn resistanceand high temperature mechanical property and is applied to make the key parts inaircraft engine, therefore it possesses huge applying potential in aerospace industry.Because the high temperature plasticity of this alloy is poor and likely to crack in thecogging process, it is necessary to study hot deformation behavior of the alloysystematically in order to obtain a suitable parameter range of hot deformation process.In this research, the compression test with constant temperature and strain rate iscarried out by using the hot working simulator in the temperature range of950～1100℃and strain rate range of0.001～1s-1. On the base of the data of the test, the influence ofstrain rate and temperature on flow stress of as-cast Ti40burn resistant titanium alloy isanalysed, and the results show that the flow stress is increasing with the increase ofstrain rate and the decrease of temperature. The suitable hot working parameter isidentified preliminarily in the ranges of950～1050℃and0.001～0.01s-1,1050～1100℃and0.001～1s-1. The deformation activity energy are calculated separately based onsteady stress and maximum stress, namely,399.2KJ/Moland404.8KJ/Mol, whichindicates that the process of hot compression is not only controlled by the self-diffusionof titanium atoms.Based on dynamic material model theory, the processing maps of Ti40burnresistant titanium alloy are drawn by using Prasad flow instability criterion and Murtyflow instability criterion. The analysis of processing maps and observation of deformedmicrostructure show that the two types of processing maps drawn by using two kinds ofinstability criterions are approximately the same and both of them can be used toidentify the flow instability area and flow stability area. Because the instability area inthe processing map based on Prasad instability criterion is bigger than that based onMurty flow instability criterion, the optimized results obtained from the processing mapbased on Prasad instability criterion is much safer in actual production. The forgingprocess stability regions optimized from the processing maps based on Prasad instabilitycriterion are1070～1100℃and0.079～1.0s-1,950～1100℃and0.001～0.0794s-1,and the better forging process parameter ranges are1080～1100℃and0.16～1s-1,1000～1100℃and0.001～0.018s-1, and the best forging process parameter are near1100℃and1.0s-1,1100℃and0.001s-1.The observation of deformed microstructure shows the main hot deformation mechanism in instability region is flow localization and the hot deformationmechanisms corresponding to two better forging process regions are identified asmeta-dynamic recrystallization and continuous dynamic recrystallization, respectively.The rest region is corresponding to the mechanism of dynamic recovery companiedwith nucleation of recrystallization. In the two better forging process regions, the onelocated in lower strain rate area has a higher η value and a homogenous deformedmicrostructure with higher dynamic recrystallization level, thus this better forgingprocess region is adopted preferentially. In another word, the better forging paramterrange adopted preferentially is1000～1100℃and0.001～0.018s-1, and the bestforging process parameter is located at about1100℃and0.001s-1.