Effects of solution time on microstructure and mechanical properties of Ti-22Al-24Nb alloy

In this research, the changing rules of billet forged Ti-22 Al-24 Nb alloy with various solution time were studied, and the mechanical properties of different microstructure were tested at the room temperature. The results indicate that the(α2+O+B2) three-phase microstructure with equiaxed grains was acquired by Ti-22 Al-24 Nb alloy billet forging, and the average size of the grains was about 300 μm. With the increase of solution time, the primary lath-shaped O phase began to dissolve, and then the equiaxial α2 phase started to dissolve, but the undissolved α2/O phase began to be equiaxial and grow. The grains of original B2 phase recrystallized and grew. After the 2 h solution treatment, the recrystallization of grains was completed basically and the average size of the grains was about 100 μm. After the 2.5 h solution treatment, the strength of the alloy decreased, and the plasticity increased. However, when the solution treatment increased to 3 h, the plasticity decreased but the strength increased. The optimal solution parameters of Ti-22 Al-24 Nb alloy were the holding time of 2 h, the solution temperature of 1 000 ?C, and water cooling. Excellent comprehensive mechanical properties can be accquired under these parameters. The tensile strength, the yield strength, the elasticity modulus, the elongation, and the section shrinkage were 950 MPa, 915 MPa, 90 GPa, 15.69% and 42.28%, respectively.

A Fractal Study on Brittle-Ductile Transition forTi-24Al-11Nb Alloy

The mechanical behaviours of Ti-24Al-11Nb alloy in the brittle-ductile transition (BOT) have been investigated by using three-point bending tests. The temperature dependence of the fractal dimensions and fractal characterization of fracture surfaces are presented. The probable mechanism controlling BDT of intermetallic alloys are proposed according to fractal geometry.Additionally. it is found that there is a positive relationship between the fractal dimension and fracture toughness in BDT for Ti-24Al-11Nb

Superplasticity of a Ti-24Al-14Nb-3V-0.5Mo Intermetallic Alloy

Superplastic properties and microstructural evolution of a Ti-24Al-14Nb-3V-0.5Mo (at. pct) intermetallic alloy were studied. Optimum superplastic properties were obtained for temperatures in the interval 960℃≤5 T≤5980℃. The apparent activation energy in the superplastic regime was determined and the deformation mechanism was also discussed. Based on the studies, a curve panel with three sheets sandwich structure was fabricated successfully. The microstructures corresponding to different strain in the part were also studied.

Local deformation and processing maps of Ti-24Al-17Nb-0.5Mo alloy

The processing maps were used to identify the optimal forging parameters of Ti-24A1- 17Nb-0.5Mo alloy by evaluating the flow data according to the DMM model. The actual local strain rate and strain distribution in the samples were obtained by finite element calculations. The local microstructures of the deformed samples were related to the local deformation parameters and correlated with the processing maps at 0.3, 0.4, 0.5 and 0.6 of logarithmic strain. Flow regimes predicted by DMM analysis were then correlated with the local microstructural observations. Five domains of efficient coefficient could be distinguished. Unstable regions were microstructurally related to shear band formation within the （~2~B2 phase deformation field, and to flow localiza- tion at grain boundaries of B2 phase in the near B2 phase deformation field. Stable flow regimes were shown to be associated with dynamic globularization of the plate- like a2 in the a2＋B2 phase deformation zone, and with dynamic recrystallization of B2 in the near B2 phase deformation zone.

Effect of Hot Isostatic Pressing Loading Route on Microstructure and Mechanical Properties of Powder Metallurgy Ti_2AlNb Alloys

In this work, hot isostatic pressing （HIPing） technique was used to densify the Ti2AINb pre-alloyed powder. The influence of HIPing loading route parameters （temperature and rates of heating and pressurizing） on microstructure and properties of PM Ti2AINb alloys was studied. The results showed that HIPing loading route parameters affected the densification process and mechanical properties （especially high temper- ature rupture lifetime） of PM Ti2AINb alloys in the present work. A finite element method （FEM） model for predicting the final densification was developed and was used to optimize the HIPing procedure.

Characterization of the prior particle boundaries in a powder metallurgy Ti2AlNb alloy

Ti2 AlNb-based alloy powder metallurgy(PM)compacts were prepared via hot isostatic pressing(HIP)under relatively low temperature(920 and 980℃)and at certain pressure(130 MPa).The microstructure,composition and orientation of B2,α2 and O phases in the compacts were characterized and analyzed with an aim to investigate the effect of unsuitable HIPping parameters on the appearance of prior particle boundary(PPB),which seriously affects the mechanical properties of the alloy.The results show that moreα2 phase is the characteristics of the PPB in Ti2AlNb-based alloy when HIPped at relatively low temperature.Increasing HIPping temperature to the upper part of the two-phase region can effectively inhibit the formation of PPB.Electron backscatter diffraction measurements show the specific orientation relationship between phases,which helps us understand the origin of a2 and O phase and the corresponding transformation path.The HIPping at a higher temperature can weaken the micro-texture intensity of theα2 and O phase due to the increase of misorientation in B2 phase.Theα2 phase at cell wall keeps the Burgers orientation relationship(BOR)with the grain on one side,and does not satisfy the BOR with the other.It is found that some O phase variants inside the cell HIPped at 980℃can only maintainα2-O OR withα2 owing to theα2→O phase transformation forming the O phase,while these O variants deviate from B2-O OR with B2 phase.