Yigang Zhou

Fracture criterion for predicting surface cracking of Ti40 alloy in hot forming processes

Abstract Hot compression tests were conducted on Ti40 burn resistant titanium alloy in the temperature range of 900–1 100 °C and strain rate range of 0.01–10 s −1 to investigate its fracture behavior and critical fracture conditions in hot forming. It was observed that the failure of Ti40 alloy is attributed to longitudinal surface cracking due to severe oxidation of element V and the secondary tensile stresses. The critical fracture strain increases with increasing temperature and decreasing strain rate. From these observations and parallel FEM simulations, it was concluded that the critical fracture strain is a function of a single argument Zener-Hollomon parameter, and there is a linear relationship between them. An Oyane criterion successfully predicted the location of crack initiation. The critical fracture values also exhibit a liner relationship with ln Z . Based on these results, a new fracture criterion of Ti40 alloy based on Zener-Hollomon parameter was established.

A new high-temperature deformation strenthening and toughening process for titanium alloys

Abstract A new high-temperature deformation strengthening and toughening process for titanium alloys, which consists of near beta transus forging, rapid water quenching, high-temperature toughening and low-temperature strengthening treatment, has been developed. The materials processed by this method produce a new tri-modal microstructure, which shows a high low-cycle fatigue property, high fatigue-creep interaction life, high fracture toughness and a high service temperature without the decreasing ductility and thermal stability. The fundamentals of the new process and the strengthening and toughening mechanism have also been discussed. It is proved that the high-temperature deformation strengthening and toughening process is applicable not only to alpha-beta alloys, but also to alpha, near alpha and near beta titanium alloys.

The influence of microstructure on dwell sensitive fatigue in Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy

The fatigue behaviour of titanium alloy Ti–6.5Al–3.5Mo–1.5Zr–0.3Si (TC11) was examined at 520°C to study the effects of microstructural variation on the dwell sensitivity. Three microstructures (equiaxed, tri-modal and basketweave) were used in this study. When a 3-min dwell time was imposed at the peak of each cycle a significant fatigue life reduction was observed for all microstructures tested. Among the three microstructures, equiaxed microstructure showed the strongest fatigue life reduction. The basketweave microstructure had a little higher dwell-time fatigue life than tri-modal microstructure at low maximum stress levels. In all cases, extensive quasi-cleavage facets and planar slips with track-like dislocations have been intimately linked with the dwell sensitive fatigue response. The amount of quasi-cleavage facets and planar slips decreased with a decrease of the α phase content. A rationalization for planar slip was proposed based on the mechanism of dislocations shearing α2 particles. It is believed that α2 particle formation and oxidization effects played an important role in dislocation planar slip.

Effect of beta flecks on mechanical properties of Ti–10V–2Fe–3Al alloy

Abstract The effects of beta flecks on tensile properties and low-cycle fatigue life were investigated at room temperature for Ti–10V–2Fe–3Al alloy. It was found that beta flecks had a significant influence on tensile ductility and low-cycle fatigue life. The greater the volume fraction of beta flecks ( P A ) or maximum area of beta flecks ( S max ), the lower the tensile ductility and low-cycle fatigue life. Extensive scanning electron microscopy (SEM) and light microscopy (LM) observation showed that under tensile load, cracks preferentially nucleated at β grain boundaries of beta flecks, then grew, connected and propagated along grain boundaries to form characteristics of intergranular fracture and quasi-cleavage fracture. While under an alternating load, beta flecks acted as sites for low-cycle fatigue crack nucleation due to inhomogeneous alternating strains between soft GB α and aged beta matrix. The presence of beta flecks accelerates both the crack nucleation and early crack propagation.

Modeling the Correlation of Composition-Processing-Property for TC11 Titanium Alloy Based on Principal Component Analysis and Artificial Neural Network

In the present investigation, the correlation of composition-processing-property for TC11 titanium alloy was established using principal component analysis (PCA) and artificial neural network (ANN) based on the experimental datasets obtained from the forging experiments. During the PCA step, the feature vector is extracted by calculating the eigenvalue of correlation coefficient matrix for training dataset, and the dimension of input variables is reduced from 11 to 6 features. Thus, PCA offers an efficient method to characterize the data with a high degree of dimensionality reduction. During the ANN step, the principal components were chosen as the input parameters and the mechanical properties as the output parameters, including the ultimate tensile strength (

Characterization of hot deformation behavior of as-cast TC21 titanium alloy using processing map

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Dynamic globularization kinetics during hot working of Ti-17 alloy with initial lamellar microstructure

), yield strength (