Isothermal Aging Precipitate of TB17 Titanium Alloy

Transmission Electron Microscope (TEM), X-Ray Diffraction(XRD) and Optical Microscope(OM)were employed to investigate the aging precipitation behavior of a new type of ultra-high strength TB17 titanium alloy. The results show that during heat solution treated in the β phase field followed by aging the secondary α phase is nucleated, precipitated and grew on the β phase matrix,and the precipitated phase is lamellar structure which has burgers relation with the matrix. The secondary α phase content is increased rapidly and finally reach a steady-state as aging time increased and the final product of aging consists of α phase and β phase. there is a good linearity relationship between the content of secondary α phase and the hardness of age hardening. The TB17 titanium alloy isothermal phase transformation kinetics can be described by JMAK equation

Investigation of Dynamic Mechanical Behavior and Damage Characteristics in TC32 Alloy

The dynamic shearing experiment was been done by using split Hopkinson pressure bar(SHPB) technique in TC32 alloy with lamellar, bimodal and basket microstructures. The damage Characteristics of TC32 alloy was investigated by using optical microscope(OP) and scanning electron microscopy(SEM). The results show that the critical fracture velocity is 2400 s-1, 2700 s-1, and 2600 s-1 for lamellar, bimodal, and basket microstructures respectively. The bimodal microstructure exhibit the best Dynamic mechanical behavior compared with the other two microstructures. Adiabatic shear bands(ASBs) and microvoids initiation, growth, and coalescence to damage in adiabatic shear bands(ASBs) were observed in all of three microstructures. Also, microvoids initiation and growth are prior to the interface between ASBs and matrix. Investigation indicated that plastic flow characteristic is not obvious at the interface between ASBs and matrix, which observed long crack in lamellar microstructure. In bimodal microstructure, fibrous a adiabatic shear bands(ASBs) and surrounding region are shown. Because of strong shear deformation, the plastic flow characteristic appears clearly, and primary α phase was elongated. Microvoids initiation is also prior to the α/β phase boundaries. The damage characteristics of basket microstructure are similar to bimodal microstructure. But unlike lamellar and basket microstructures, the microvoids are initiatied when the acicular primary α phase arranged in order is perpendicular to the adiabatic shear bands(ASBs) in lamellar microstructure. ASBs is mostly consisted of equiaxed grains, and the deformation mechanism still wasn't defined

Research and Application of New Type of High Performance Titanium Alloy

With the continuous extension of the application quantity and range for titanium alloy in the fields of national aviation, space, weaponry, marine and chemical industry, etc., even more critical requirements to the comprehensive mechanical properties, low cost and process technological properties of titanium alloy have been raised. Through the alloying based on the microstructure parameters design, and the comprehensive strengthening and toughening technologies of fine grain strengthening, phase transformation and process control of high toughening, the new type of high performance titanium alloy which has good comprehensive properties of high strength and toughness, anti-fatigue, failure resistance and anti-impact has been researched and manufactured. The new titanium alloy has extended the application quantity and application level in the high end field, realized the industrial upgrading and reforming, and met the application requirements of next generation equipment

Precipitation and evolution behaviors of grain boundary α and α side plates for ultra-high strength titanium alloy during continuous cooling

In this paper, precipitation behavior and evolution mechanism of grain boundary α (αGB) and α side plates (αSP) of ultra-high strength titanium alloy are investigated. Precipitation of αGB can change original morphology of β grain boundary into irregular shapes, and it is much more obvious at slower cooling rate. The λ, which denotes the minimum value of misorientations between 12 α variants of βnBOR and αGB, is introduced to quantitatively evaluate morphology of αGB. The β phase that maintains Burgers orientation relationship (BOR) with αGB is labeled as βBOR, conversely, it is labeled as βnBOR. The deformation degree of αGB increases with the increasing λ. However, the λ is not the only factor that determines morphology of αGB, and it is also related to the angle between habit plane and grain boundary plane. Orientation of αGB is affected by β phase on both sides. The αGB maintains BOR with βBOR and the s-BOR with βnBOR. The s-BOR is defined as (0 0 0 1) plane of αGB is not parallel to (110) plane of βnBOR, but one of 〈1 1 –2 0〉 directions of αGB is parallel or close to one of βnBOR’s 〈111〉 directions

Microstructure evolution and mechanical property of a new multi-component β titanium alloy with ultrahigh strength above 1350 MPa

The microstructure evolution and precipitation behavior of a multi-component β titanium alloy (namely TB17) were investigated through various characterization methods. The results show that with the increase of the solution temperature, the coarse lamellar α phase (αl) and fine secondary α phase (αs) existed in the original as-forged TB17 alloy decrease. At the same time, the molybdenum equivalent value of the β matrix also decreases gradually, leading to the increase of αs phase during the following aging process. For the aged samples, the micro-strain accumulated in the β matrix resulted from phase transformation strain exhibits an increasing trend as the solution treatment temperature rises, highly depending on the volume fraction of αs phase. When the alloy is subjected to a solution treatment at temperature of 805 °C plus aging, it can achieve a good combination of high strength of 1375 MPa and considerable ductility due to mixed microstructure of suitable amount of micro-scale αl and nano-scale αs precipitates. The strength is further improved by increasing the solution temperature (from α+β to β field), which is attributed to higher volume fraction of fine αs precipitates formed during aging that can effectively hinder dislocation slip and induce micro-strain. Morphological features of the fracture surfaces are also discussed against the different microstructural morphologies, revealing the fracture mechanism of TB17 alloy under different heat treatment conditions. The current work could contribute to a better understanding of phase transformation behavior and strengthening mechanism in TB17 alloy