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Investigation on the formation of central damage in cross wedge rolling of GH4169 alloy

Li Junling, Li Zheng, Wang Baoyu, Sun Chaoyang, Chen Ping, Fang Shuang

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 3

art. no. e204, 2023

EN

Cross wedge rolling process provides a new way with short production chain and precise control for high-performance blade preforming used in aeroengine, but the issue of central damage needs to be paid attention and investigated. Therefore, this paper aims to understand the formation mechanism of central damage on CWR of GH4169 alloy. The uniaxial hot tensile test and CWR experiments were carried out to explore the high-temperature deformation behavior of GH4169 alloy, as well as the central damage of GH4169 alloy CWR process. Moreover, the finite element model was established and used to analyze the evolution of stress and strain at different position. The results showed that central part of the workpiece is in the state of higher stress triaxiality η, which is easy to cause damage. And the micro-holes in the center of workpiece mainly nucleated around the detached NbC carbide. Meanwhile, the first principal stress and the maximum shear stress are the dominant factors which affect the central damage. Therefore, a novel damage criterion suitable for CWR of GH4169 alloy was developed with considering the effect of stress triaxiality η and the sensitivities of deformation temperature and strain rate on the central damage evolution. In addition, initial forming temperature T0 is the most important factor affecting the central damage, and the maximum area reduction and rolling speed n are related to the initial deformation temperature T0. And in order to inhibit the damage, the initial forming temperature should be controlled below 1020℃, and the area reduction and rolling speed should not be higher than 55% and 10r/min, respectively.

2

Microstructure and mechanical properties of TC4 titanium alloy hollow shaft formed by cross wedge rolling

Feng Pengni, Yang Cuiping, Wang Baoyu, Li Junling, Liu Ronge

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 3

737--751

EN

Production of hollow shafts satisfying mechanical performance requirements can well meet the needs of lightweight. The purpose of this work is to investigate the effect of cross wedge rolling (CWR) process parameters on microstructure and mechanical properties of TC4 titanium alloy hollow shafts, so as to ensure the feasibility of forming TC4 titanium alloy hollow shaft by CWR. The results demonstrate that the initial deformation temperature, area reduction, wall thickness, and mandrel have significant effects on the volume fraction of primary alpha phase (fα_p), morphology of alpha phase and interface of alpha/beta phase. The decrease of the fα_p, the increase of fine secondary alpha phase content and the increase of the number of alpha/beta phase interfaces can increase the strength of TC4 alloy hollow shafts, but decrease the elongation. When the initial deformation temperature is 950 °C, the contribution of the thick secondary alpha phase is similar to that of the primary alpha phase, resulting in the decrease of strength. The strength is further improved owing to the grain refinement with the increase of area reduction to 60%. The strength decreases as the wall thickness increases owing to the non-uniform microstructure distribution, which can be improved by increasing the area reduction appropriately. The comprehensive mechanical properties of the workpiece rolled with a mandrel are evidently higher than that rolled without a mandrel. Under any forming condition in this work, every fracture surface is covered with abundant dimples and voids, showing good ductile fracture characteristics.

3

Investigation of the microstructure evolution and mechanical properties of a TC6 alloy blade preform produced by cross wedge rolling

Li Junling, Wang Baoyu, Fang Shuang, Chen Ping

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 3

91--101

EN

Cross wedge rolling (CWR) is one of the most effective plastic deformation methods utilized for the production of shaft parts or non-shaft preforms with refined grains and improved mechanical properties. The main goal of this work was to study the influence of CWR process parameters on the microstructure evolution and mechanical properties of a TC6 alloy and determine the suitable process parameters for a TC6 alloy blade preform fabricated with CWR. The results showed that the volume fraction of the equiaxed α phase (fα_e) decreased from ~ 0.38 to ~ 0.04 by increasing the initial deformation temperature, and the elongation (El) also decreased from ~ 19.6 to ~ 11.8% because dislocation slip first started in the equiaxed grains and then dispersed into the adjacent grains. Thus, additional equiaxed grains contributed to an increased plasticity. Moreover, with an increasing area reduction, the value of fα_e increased from ~ 0.14 to ~ 0.31, and the grain refinement and microstructure uniformity also increased. In addition, the El was significantly reduced by over 50%, but the ultimate tensile strength (UTS) and yield strength (YS) increased under WC (water cooling) conditions due to the precipitation of the acicular secondary α phase and pinning effect of the small equiaxed α phase. Based on the determined suitable parameters, the TC6 alloy blade preform was successfully manufactured by CWR, the microstructure was evenly distributed, and the UTS, YS and El were 1120.1 MPa, 1020.9 MPa and 15.2%, respectively, which meet the current technical requirements.

4

Numerical and experimental research on cross wedge rolling hollow shafts with a variable inner diameter

Shen Jinxia, Wang Baoyu, Zhou Xu, Li Junling

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 4

1497--1510

EN

The precise forming of inner hole has been a major technical difficulty in the cross wedge rolling (CWR) of hollow shaft. This paper proposes a new process to form hollow shafts with variable inner diameters by using the CWR with mandrel control. The forming characteristics and dimension precision of this process are analyzed by combining finite element modelling (FEM) and forming trials. The hole step of hollow shaft with variable inner diameter is formed in a spiral pattern. The helixes result in many micro-steps in hole step when forming the right-angle inner step. The metal flow lines demonstrated that mandrel step hindered the axial metal flow of inner hole and the metals were accumulated in hole step. The rolling load increases in the process of forming hole step. The mandrel is subjected to axial load when hole contacts the mandrel step. The roundness can be improved by reducing the mandrel diameter in knifing position. The axial accuracy of inner diameter can be classed as three parts: hole expansion, stable rolling, hole shrinkage. The compensated mandrel was designed to improve axial precision of inner diameter. The results showed that the inner hole dimension can be effectively controlled.