Papers by Author: Wen Zhe Chen

Abstract: Three groups of commercial 5052 Al alloy sheets were subjected to groove pressing (GP) at room temperature using parallel GP, 180° cross GP and 90° cross GP, respectively. Mechanical properties and fracture modes of as-annealed and GPed samples were investigated. The microhardness of the samples processed by parallel GP increases by a factor of about 1.6 compared to the as-annealed state, and that of the samples processed by cross GP is higher. The ultimate tensile strength (UTS) increases significantly after GP, while the elongation decreases. But they are strongly dependence on the number of GP passes and the pressing modes. Besides, fracture surface morphology demonstrates that the fracture mode is ductile even after four passes. With increasing the number of GP pass, the amount of small dimples increases, and the dimples become shallow and more uniform.

Abstract: Mechanical properties of the TiAl alloy produced by centrifugal spray deposition (CSD), compared to that produced by ingot metallurgy (IM), were investigated at different temperatures from 293 to 973K. The result shows that the ultimate strength, yield strength and plasticity of the CSD TiAl alloys, with excellent compression properties and plasticity, are higher than those of as-cast TiAl alloys at room temperature as well as at high temperature. There exists a critical temperature of 873K in the relationship between strength and temperature, in which strength increases with increasing temperature above 873K. The effects of CSD on mechanical properties of the TiAl alloy are discussed, and the higher strength with moderate ductility achieved is because of the finer lamellar structure got in the CSD processing, and this structure is also believed to be beneficial to ductility.

Abstract: The strengthening effects of the Cu-80 wt.% W (CuW80) alloy and the copper parts in Cu-80wt.% W /Cu (CuW80/Cu) solid contact alloy, which was sintered and infiltrated prepared by powder metallurgy, were investigated. The effects of different compressive deformation on microstructure and properties of the CuW80 were studied. Furthermore, the influences of HextrusionH on copper parts, the carrier material of the solid contact alloy CuW80/Cu were also investigated. The results show that the tungsten and copper phases are closely bonded by physical bond in the form of pseudo-alloy and the copper phase is homogeneously dispersed within the tungsten framework. The hardness of the CuW80 increases with increasing compressive deformation. Especially, the hardness of the copper parts in CuW80/Cu increases remarkably after extrusion and the maximum value can reach 200%. The hardness increases from the inner to the surface and is proportional to the distance departing from the interface of the CuW80 and Cu. TEM observation shows that the dislocation tangles exist, even inside the dislocation cell, in copper grains after extrusion.

Abstract: The as-cast microstructure feature of Al sheet with high forming properties used for pressure can manufacturing pre-treated by different melt-treatment technique was observed and analyzed by SEM, EDAX, TEM and selected area electron diffraction (SAED), etc. It was found that the oxide inclusions in Al sheet were mainly γ-Al2O3, and the Fe-rich impurity phases in the sheet mainly Al3Fe, T1(Al12Fe3Si) or (AlFeSiRE). The crystal structure of (AlFeSiRE) phase was too complicated to be determined. The effect of melt-treatment technique on the as-cast microstructure of the sheet was remarkable. There were a number of oxide inclusions in the Al sheet before or after conventional melt-treatment, which distributed non-uniformly and gathered together in larger block shape with the size of about 10-40μm. The Fe-rich impurity phases in the sheet were mainly Al3Fe and T1, and a few of the meta-stable phase Al6Fe existed in the sheet. These Fe-rich impurity phases appeared in a coarse, long needle/flake or skeletal form, and were easily to gather together with oxide inclusions. When the Al sheet was treated by high-efficient melt-treatment, the amout of oxide inclusions was decreased obviously, and these inclusions distributed more uniformly in the tiny granular form (about or less than 4μm). The Fe-rich impurity phases were mainly (AlFeSiRE), and a small amount of Al3Fe phases also existed in the material. The (AlFeSiRE) phases distributed uniformly along grain boundary in tiny group/sphere or short stick form. No congregation of Fe-rich phases with oxide inclusions was found in the material.

Abstract: Studies of the influences of symmetric tensile-compressive low cyclic fatigue behavior and dynamic strain aging (DSA) pre-treatment on H68 brass were made. The results showed that the cyclic softening was the main factor that controlled the fatigue life after various pre-treatments. The process of cyclic softening was believed to be related to the change of dislocation configuration. TEM observation indicated that the uniform and stable dislocation networks with high density formed after DSA pre-treatment, which increased the deformation stress, decreased the cyclic strain. The cyclic softening was caused by the low dislocation density and elongated cell structure with low energy

Abstract: The Al sheet used for pressure can manufacture (or called Al piece) was prepared by different melt-treatment techniques and using the lower grade commercial purity raw Al (Al99.5). And the influence laws of melt-treatment techniques on the metallurgical quality and mechanical properties of Al piece were investigated. It is found that high-efficient melt-treatment technique improves the metallurgical quality of Al piece remarkably, that is, the rate of removing inclusions and the extent of lowering porosity amount to about 66.6% and 87.0%, respectively, and as-cast mean grain diameter decrease to a great extent, and the coarse and long needle/flake Fe-rich impurity phases transform into complex compounds of tiny, sphere/short stick form, which makes fracture mechanism of the material be transformed into the congregation of transgranular micro-hole, thus raising mechanical properties of this material remarkably. Its metallurgical quality and mechanical properties have reached or exceeded the level of present products. It is feasible that Al piece is made by using the lower grade commercial purity raw Al. The viewpoint that the purification is the fundamental and key process, i.e., the basic of modification and grain refinement processes, has been also further tested and verified.

Abstract: Ti-48Al-2Mn-2Nb alloy was produced by “centrifugal spray deposition” (CSD), and then hot isostatic pressing (HIP) was employed to remove the porosity formed by CSD. The effects of CSD and HIP processing on the mechanical properties and microstructure of the TiAl alloy were investigated. The results show that the CSD and HIP processing can both improve the strength, plasticity of the TiAl alloy, and the tensile elongation values of the CSD or HIP samples are around 3%, which are better than those of as-cast TiAl alloys in room temperature. Especially, they show more excellent compressive properties at ambient temperature with a compressive ratio of 33.8% and compressive strength of 2210MPa for the CSD samples, and a compressive ratio of 37.8% and compressive strength of 2348MPa for the HIP samples. The CSD processing also improves the fracture toughness of TiAl alloy, which is much higher than that of the HIP processing, while the HIP processing seems to be beneficial the ductility and plasticity as having a duplex structure. The effects of CSD and HIP processing on microstructure and properties of TiAl alloys are discussed to understand the deformation and fracture process of the alloy.