The Microstructure And Mechanical Properties Of New TiAlCrFe Low Cost Titanium Alloy

In this paper, new type of low cost TiAlCrFe alloys were designed and melted by using bargain Cr-Fe alloy as master alloy. The costs of raw materials for these new alloys are three-quarters to eighty percent of TC4. Observation and analysis of the microstructure of alloys under different heat treatment conditions were done by employing OM, SEM, TEM, and XRD. The effects of cooling ways, heating temperature and holding time on mechanical properties of alloys were discussed. Thermal simulation experiments were carried out for some well-selected alloys to explore the processing technology during hot working. The main results are as follows:Cooling methods, heating temperature and holding time all have certain effect on the microstructure of alloys. The microstructure consists of a phase and β phase when TCF, TACF, TACF1, TACFB and TACF2alloys were heat treated at Tp+20℃and then cooled by air cooling or furnace cooling; β and a martensite when they were heat treated at Tp+20℃and then water quenched except that co also observed in TCF and TACF alloys,β phase,ω phase and a martensite were observed in TACF3alloy after air cooling or quenching in water while a phase and (3phase after furnace-cooled. TiB precipitated in TACFB alloy under different conditions and it could refine ingot microstructure of alloys. The grain size of alloys increased with increasing holding time and heating temperature when the alloys were heat treated above transus temperature and then air cooled. β phase and primary a were observed when the alloys heated below transus temperature, and primary a transformed to β gradually with temperature increasing.The amounts of alloying elements, cooling methods, heating temperature and holding time have certain effect on tensile properties of alloys. Because of ω phase, TCF and TACF alloys obtained the highest strength when they were water quenched; TACF1, TACFB, TACF2and TACF3alloys obtained the highest strength when they were air cooled, with the highest tensile strength is1260MPa of TACF3alloy. The strength of TACF, TACF2, TACFB and TACF3alloys changed a little with increasing holding time when they were heat treated above transus temperature. The strength of all of six alloys changed a little with increasing heating temperature. The strength of TACF2and TACF3alloys decreased gradually with increasing time and temperature during direct aging, and TACF3alloy directly aged at525℃for8hours obtained the highest strength; with tensile strength and elongation are1415MPa and7.0%respectively.Strain rates and deformation temperature have a significant influence on true stress-true strain curves for TACF1and TACFB alloys. At the initial stage of hot compression, true stress increased rapidly with increasing true strain, and then decreased after reaching the peak value, and finally reached a constant value. It was found that true stress increased with increasing true strain at different temperature, and decreased with increasing deformation temperature at different strain rates.Constitutive equations were established for TACF1and TACFB alloys based on Arrhenius constitutive equation. When deformed under the same condition, TACF1alloy required less activation energy than TACFB alloy. From the processing map of TACF1and TACFB alloys at the strain of0.7, it could be concluded that TACF1alloy can be processed at various strain rates from900℃to950℃, and TACFB alloy can be processed at every field except at strain rate of1.0s-1from870℃to940℃. The trend of dynamic recrystallization became more and more obviously with increasing deformation temperature and strain rates, and fine recrystallized grains deformed at the intersection of grains and grain boundary. In these experiments, the dynamic recrystallization was incomplete.