An investigation of normal and submerged condition on microstructural and tribological properties of friction stir processed AZ91-D magnesium alloy

A comparative study of micro-structural transformations and tribological properties of the friction stir processed AZ91-D magnesium (Mg) alloy in normal friction stir processing (NFSP) and submerged friction stir processing (SFSP) conditions was carried out. The optimum parameters used for processing were tool rotational speed of 1000?rpm/min, 50?mm/min of transverse speed and 6 numbers of passes. A significant reduction in grain size (28.7% and 13.1%) and increase in micro-hardness (14.55% and 8.92%) along depth and width of stir zone (SZ) of SFSPed specimen has been achieved as compared to NFSPed specimens. This change can be attributed to the dynamic recrystallisation and removal of excess frictional heat leading to inhibited post-grain growth in the processed alloy. Pin-on-disc sliding wear testing was conducted to compare the wear performance of NFSPed and SFSPed specimens. The SFSPed specimen has shown an improved wear resistance as compared to NFSPed specimens. The major prevailing wear mechanisms were abrasion, delamination, oxidation and mild plastic deformation.     

Effects of Al contents on microstructure and properties of hot-dip Zn-Al alloy coatings on hydrogen reduced hot-rolled steel without acid pickling

A new hot-dip galvanizing method was employed on hot-rolled low carbon steel. The effects of Al contents on microstructure, micro-hardness and corrosion resistance of Zn-Al alloy coatings were systematically investigated. Phase composition, microstructure and element distribution in Zn-Al alloy coatings were analyzed using X-ray diffraction (XRD) and electron probe micro analysis (EPMA), respectively. It is found that Al content (0. 6–6. 0 wt. %) in galvanizing zinc affects surface quality and adhesion between coatings and matrix in the newly developed method. In addition, with increasing Al content, micro-hardness significantly increased due to the increase in Zn-Al eutectoid phases. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) also revealed that increase in Al plays a noticeable role in improving the corrosion resistance of Zn-Al alloy coatings.     

Surface characteristics of Ti-6Al-4V by SiC abrasive-mixed EDM with magnetic stirring

Ti-6Al-4V is widely used in aerospace, biomedical applications and in many corrosive environments. However, titanium alloy has low hardness and poor wear resistance. This paper introduces a machining method of SiC abrasive-mixed electrical discharge machining (EDM) with magnetic stirring. Structural features and chemical composition were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). Micro-hardness distribution on the cross section was measured with an FM800 micro-hardness tester. The influence of pulse width and pulse peak current on the formation of the surface hardening layer is analyzed. The results show that a continuous strengthened layer was formed during the SiC abrasive-mixed EDM process. The hardness of the formed layer was significantly improved because of the formation of TiC and TiSi₂ phases on the machined surface. With the increase of pulse width, the thickness of the strengthened layer increases and the quality becomes better.     

Optimization of the shear strengths of ultrasonically consolidated Ti/Al 3003 dual-material structures

The interfacial bonding between layers in ultrasonically consolidated structures is poor for some material combinations, resulting in relatively low bond strength. This makes resultant parts unsuitable for structural applications. This work discusses a study of the effects of post process heat treatment of ultrasonically consolidated commercially pure titanium and aluminum alloy 3003 dual-material systems. The lap shear strengths of as-consolidated specimens as well as heat treated ones were tested. The results show that there is significant improvement of the strengths of post processed specimens over the as-consolidated ones. The improvement is as a result of stress relieving of the strain hardened interface between the two materials and some interactions of the base materials across the interfacial boundaries at elevated temperatures, leading to stronger bonds. The study highlights the role of post process heat treatments for improving the mechanical properties of ultrasonically consolidated structures.     

密封圈的失效分析

经碳氮共渗淬、回火热处理的密封圈,其表面获得高的硬度和良好的耐磨性,心部具有良好的综合性能,但在使用过程中易发生变形而破裂.采用金相检验和显微硬度测定等方法对失效件进行了分析,并与合格件进行比较.结果表明,导致密封圈变形而破裂的原因是选用的ST12钢含碳量太低,应选用含碳量和强度稍高的材料来制造.     

Fabrication of Co-Based Coatings on Titanium Alloy by Laser Cladding with CeO2 Addition

In this study, Co-based laser cladding coatings reinforced by multiple phases were fabricated on titanium alloy. Co42 Co-based self-fluxing alloy, B₄C, and CeO₂ mixed powders were used as the precursor materials. The coatings were mainly composed of γ-Co/Ni, CoTi₂, CoTi, NiTi, TiC, Cr₇C₃, TiB₂, and TiB phases. A typical TiB₂/Cr₇C₃/TiC composite structure was chosen. It was found that CeO₂ did not influence the phase types of the coating significantly, but was effective in refining the microstructure and enhancing the microhardness and dry sliding wear resistance. Compared with the Ti-6Al-4V titanium alloy, the microhardness and wear resistance of the composite coatings were enhanced by 3.44–4.21 times and 14.26–16.87 times, respectively.     

Identification of constitutive model for rubber elasticity from micro-indentation tests on natural rubber and validation by macroscopic tests

Micro-hardness testing is widely used to measure the materials local response and is very valuable to describe gradients of physical properties. For polymers, the most common use is to measure a scalar value (hardness or modulus), which gives access to useful qualitative information but can clearly not be used to identify local constitutive models, strongly needed to achieve the numerical simulation of heterogeneous massive parts. In this study, load/displacement curves obtained at a micro-scale are used to identify the parameters of an Edwards-Vilgis hyperelastic model. The protocol proposed is coupling FE simulations achieved with Abaqus and optimization procedures using the dedicated software Boss Quattro. In order to limit the microstructure and viscous effects, the material studied is an unfilled natural rubber which exhibits a behavior very close to perfect hyperelasticity. Several numerical parameters (indent geometry, friction, thickness, …) as well as experimental protocols were tested in order to check the protocol reliability. The identified parameters are used to simulate macroscopic tests (tensile, compression and pure shear tests). The agreement with experimental data is very good, which is rarely found in the literature and which validates several numerical assumptions.     

溅射TiN薄膜的机械性能与光学性质

运用直流磁控溅射技术,在加温与具有偏压的硬质合金与奥氏体不锈钢衬底上,在N_2与Ar压强比在3%～13%内沉积TiN薄膜。对这种TiN薄膜的机械与光学性能作了研究,测定了它们的表面粗糙度、显微硬度可达23520N/mm~2和划刻临界负载可达80N,给出了TiN薄膜晶格常数变化与SEM的断面形貌图。测定了两种基体上TiN薄膜的近于垂直的镜反射率、漫反射率与总反射率。还确定了TiN薄膜的光学常数n—折射率,k—消光系数。     

快速凝固法制备Mg-Al-Ca合金薄带

通过单辊快淬法制备了Mg-8.2Al-4.7Ca合金薄带,采用XRF、XRD、金相显微分析、显微硬度测量等分析方法研究了其凝固组织及相结构,以及转速对镁合金条带厚度和显微硬度的影响。研究结果表明,急冷快速凝固条件下,合金形成非晶相 细小hcp-Mg(Al,Ca)相;镁合金薄带显微组织沿厚度方向分为近辊面细晶区、内部柱状晶和自由面粗晶区;随着辊速的提高,晶粒不断细化,薄带的硬度不断提高。晶粒细化是显微硬度提高的主要原因。     

Fabrication of Ni60–SiC coating on carbon steel for improving friction,corrosion properties

The Ni60 and SiC–Ni60 composite coatings were successfully obtained by high-frequency inductive cladding on the AISI 1045 steel surface. The influence of SiC nanoparticles on the morphologies, phase composition, micro-hardness, wear resistance and corrosion resistance of the coatings were investigated systematically. An ultrasonic-assisted method was pre-treated for homogenising coating. The performance tests of coatings indicated that high-quality metallurgical bonding was formed under the optimised parameters. The average micro-hardness of Ni60 and SiC–Ni60 coatings was 765.6 and 1072.4?HV, respectively. The corresponding wear resistance was also measured, and the composite coating showed a much lower friction coefficient and wear rate. The corrosion resistance of the coatings was evidently improved by the addition of SiC nanoparticles.