Some observations on hardness measurements of particulate-reinforced 6061 aluminum metal matrix composites

Hardness measurements on a series of particulate- reinforced metal matrix composites in a solution treated and T- 6 condition were carried out using a Vickers microhardness tester at 25-, 50-, 100-, 200-, 300-, and 500-g indenter loads and a Vickers macrohardness tester at an indenter load of 5 kg. It appears that the presence of the particles makes a contribution to the hardness measurement, the degree of which depends on the size and distribution of the particles, and also the indentation load. Although some trends are observed, there is no predictable effect of the material and test parameter on the hardness values.     

Hardness of hexagonal tungsten carbide crystals as a function of orientation

A new depth-sensing microhardness mapping system has been used to measure the variation in microhardness with applied load and orientation of WC crystals. The orientations of the individual crystals were measured using an electron backscatter diffraction (EBSD) technique. The WC crystals were ～100 μm in size, embedded in a copper alloy matrix, to enable arrays of multiple microhardness indents to be implanted in each grain, thus generating good statistical validity for the results. It was found that the most significant effect on microhardness was the angle between the plane of measurement and either the basal or prism planes. A simple cosine rule, in line with resolved shear stresses, was used to correlate the data. The results are compared with previous studies using Knoop, Vickers and Berkovitch indenters, and some discussion is included of observed deformation around indentations using electron imaging associated with the EBSD technique.     

Excellent mechanical properties of metastable c-WN fabricated at high pressure and high temperature

Tungsten nitrides (WNs) are promising functional materials with high hardness, but the greatest challenge is to synthesize stoichiometric and bulk materials. In this paper, bulk tungsten mononitride (c-WN) with sodium chloride structure, which is a metastable phase, has been successfully synthesized at high pressure and high temperature (HPHT) using W₃N₄ as precursor. It is found that synergistic effect of pressure and temperature was useful to control the complete decomposition of W₃N₄ and to suppress further decomposing of as-synthesized c-WN. The compression ability and Vickers hardness were investigated by in situ high pressure X-ray diffraction (XRD) and Vickers microhardness tests, respectively. It is worth noting that the bulk modulus of c-WN is 422.9 ± 6.7 GPa, which is comparable to diamond. The Vickers hardness, 29 GPa obtained under an applied load of 0.49 N, is nearly 45% higher than that of TiN which is widely used as hard wear protective coatings. The excellent mechanical properties of c-WN may be ascribed to strong pd hybridization which has been further proved by XPS.     

激光功率对激光熔覆FeCoBSiNb涂层组织和性能的影响

采用高功率半导体激光器在低碳钢表面激光熔覆了Fe-Co-B-Si-Nb合金涂层。借助光学显微镜、X射线衍射仪(XRD)、扫描电子显微镜(SEM)以及数显维氏硬度计,探讨了激光功率对涂层稀释率、物相组成、微观组织及其显微硬度的影响。试验结果表明:在其它工艺参数一定的情况下,激光功率越大,涂层稀释率越大;激光功率为1 050W时,涂层中部的物相分析表现为具有非晶特征的漫散射峰,微观组织由颗粒状晶体和无组织形貌特征的灰色基底组成,随着激光功率的增大,涂层中部的晶化相衍射峰逐渐增多增强,微观组织中出现"雪花"状晶体;涂层和基材结合区的微观组织以具有外延生长特征的平面晶和柱状树枝晶为主;涂层的平均硬度随激光功率的增大而降低。     

Photothermal,Structural, and Microstructural Characterization of SAE4320H Automotive Steel

SAE4320H steel was characterized by photothermal radiometry spectroscopy, scanning electron microscopy, x-ray diffraction, and Vickers microhardness, to study metallurgical property changes as a result of the annealing heat treatment. Photothermal radiometry (PTR) images of hot forged and annealed SAE4320H steel were obtained to study the thermal changes, as a consequence of metallurgical microstructure changes that were produced by the heat treatment conditions. X-ray diffraction showed that the annealing process improves the crystalline quality of the SAE4320H steel and releases of any thermal stress. Widmanstatten microstructure was identified as a typical structure after the forging process. The Widmanstatten is a metallographic microstructure transformation to ferrite and pearlite which affected SAE4320H steel hardness and thermal properties. Vickers test showed that the hardness decreases as a result of the annealing process. A positive correlation between Vickers microhardness and PTR amplitude images was found, indicating that the annealing process increases the PTR signal. This methodology allows the determination of the changes in the Vickers microhardness from a non-contact and remote method as in PTR.     

Nickel Electrodeposition from all-Sulphate and all-Chloride baths. Texture and Microhardness

In the nickel electrocrystallization process there appears a strong specific inhibition of crystal growth. Various chemical species, such as Ni(OH)₂ gaseous H₂ or H_ads which exist or are formed in the metal-electrolyte interface according to the electrolysis conditions, are selectively adsorbed in the continually regenerated metallic surface and determine the texture of the electrodeposits.

The aim of this work is to study the correlation between the texture and the microhardness of nickel deposits. The preferred orientation of the deposits, prepared from all sulphate and all chloride baths, was studied by X-ray diffractometry and the corresponding texture diagrams were traced as a function of the solution pH and the cathodic current density. The microhardness of the deposits was determined by the Vickers method.

It is shown that the textures and the microhardness of the deposits depend on the electrolysis conditions. but the hardness seems to be independent of the crystallite orientation, in spite of the related bibliographic references. The preferred orientations and the microhardness of the nickel deposits are produced by the same cause: the specific inhibition of the cathodic surface during the electrodeposition determines the orientation of the crystallites, produces deformation of the crystal lattice and increases the hardness of the deposits.     

A Method for Measuring the Hardness of the Surface Layer on Hot Forging Dies Using a Nanoindenter

The properties and characteristics of the surface layer of forging dies are critical for understanding and controlling wear. However, the surface layer is very thin, and appropriate property measurements are difficult to obtain. The objective of the present study is to determine if nanoindenter testing provides a reliable method, which could be used to measure the surface hardness in forging die steels. To test the reliability of nanoindenter testing, nanoindenter values for two quenched and tempered steels (FX and H13) are compared to microhardness and macrohardness values. These steels were heat treated for various times to produce specimens with different values of hardness. The heat-treated specimens were tested using three different instruments—a Rockwell hardness tester for macrohardness, a Vickers hardness tester for microhardness, and a nanoindenter tester for fine scale evaluation of hardness. The results of this study indicate that nanoindenter values obtained using a Nanoindenter XP Machine with a Berkovich indenter reliably correlate with Rockwell C macrohardness values, and with Vickers HV microhardness values. Consequently, nanoindenter testing can provide reliable results for analyzing the surface layer of hot forging dies.     

灰口铸铁镍基等离子熔覆层组织和性能

采用等离子弧粉末熔覆技术在磨损的灰口铸铁发动机缸体上制备了Ni基熔覆层.通过光学金相显微镜和扫描电镜观察分析了熔覆层显微组织和形貌,并利用维氏硬度计测试了熔覆层的显微硬度.试验测试结果表明:等离子弧粉末熔覆制备的熔覆层为奥氏体组织,没有出现灰口铸铁堆焊中经常产生的自口组织;熔覆层硬度与母材硬度相一致,达到了铸铁缸体尺寸修复层与母材硬度相近的要求.     

Microstructure and properties of thin wall by laser cladding forming

Laser cladding forming is a layer additive manufacturing technique and can be used to fabricate three-dimensional fully dense metal components directly from the CAD model with neither mould nor tool. It has shown extensive application on many fields and has been intensively developed. An investigation of laser cladding forming for Ni-based tungsten carbides (WC) thin wall is presented in this paper. The phase constitution, microstructure and microhardness were investigated by X-ray diffractometer, energy dispersion spectroscopy, scanning electron microscope and Vickers hardness tester. The characteristics of the thin wall were studied also. The results showed that the undissolved tungsten carbides uniformly dispersed in the matrix of the Ni-based alloy. A preferable bonding mode between WC particle and nickel-based alloy matrix was observed in the thin wall. The Vickers hardness across the longitudinal section of the sample in the height-direction shows a periodical fluctuation due to the secondary heating.     

Ultrasonic and hardness measurements for ultrahigh pressure prepared WB ceramics

The Vickers hardness of pressure synthesized WB compacts was measured using a diamond indentation method. Under the applied load of 4.9 N, our test gave a maximum Vickers hardness of 30.1 GPa for WB compacts. The hardness of WC-8 wt.% Co composites was also measured under the same load for comparison, which was found to be much lower than that of WB. The Young's modulus, bulk modulus, and shear modulus of WB and WC-8 wt.% Co were further investigated by ultrasonic measurements. The results suggest that WB might be a promising hard alloy material for industrial applications.     

机械诱导金属表面再生层性能分析

利用羟基硅酸盐减磨、再生的摩擦学特性,通过机械摩擦磨损诱导金属(45钢)表面生成一层再生层。用扫描电子显微镜表征再生层的厚度,并用能谱分析仪和X射线光电子能谱仪分析再生层的元素组成和化学状态,用维氏硬度仪和洛氏压痕法测试其显微硬度和表层结合力。结果显示:当添加剂羟基硅酸盐质量分数为10.5%时,金属磨损量最小,再生层厚度最大;再生层主要含有C、O、Fe、Cr等4种元素,这些元素以石墨碳和金属氧化物形式存在;对再生层进行力学性能测试,再生层维氏硬度为648.8 HV_(0.3),为基体的1.7倍;表层结合力临界载荷Pc约为150 kg,与基体结合性能好。     

材料涂层(合金层)硬度的测量方法与技巧

介绍了活塞、活塞环、轴瓦涂层硬度的试样制备过程及注意要点,强调正确制备试样是测量涂层硬度的基础。分析了维氏硬度测量误差的来源,指出试验载荷选择遵循的原则,并分别就轴瓦涂层硬度、活塞环涂层硬度、活塞涂层硬度的测量方法进行了讨论,说明正确选择涂层硬度的测量方法至关重要。     

The Study of Plasma Nitriding of AISI304 Stainless Steel

This paper presents results on the plasma nitriding of AISI 304 stainless steel at different temperatures in NH3gas. The working pressure was 100～200 Pa and the discharge voltage was 700～800V. The phase of nltrided layer formed on the surface was confirmed by X-ray diffraction. The hardness of the samples was measured by using a Vickers microhardness tester with the load of 50g. After nitriding at about 400℃ for two hours a nitrided layer consisting of single γN phase with thickness of 51.tm was obtained. Microhardness measurements showed significant increase in the hardness from 240 HV (for untreated samples) up to 950 HV (for nltrided samples at temperature of 420℃). The phase composition, the thickness, the microstructure and the surface topography of the nltrided layer as well as its properties depend essentially on the process parameters.     

磁兼容Au-25Pt合金的组织结构及综合性能

Au-Pt合金具有优异的MRI磁兼容性、良好的生物兼容性、高的耐蚀性等优点,在医用材料领域具有巨大的应用前景。采用X射线衍射仪、金相显微镜、维氏显微硬度仪和综合物性测量系统等,研究冷加工过程Au-25Pt合金丝材的组织结构演变及其对体积磁化率和维氏硬度的影响,为制备综合性能优异的Au-Pt合金探索有效途径。结果表明,固溶处理后的Au-25Pt合金为面心立方结构的单相固溶体,经30%～70%冷变形后,没有其它相产生。冷加工变形显著增加了Au-25Pt合金的维氏硬度,尤其在冷加工初期(<30%变形量),但对磁化率影响很小。冷变形Au-25Pt合金不仅具有接近人体组织的体积磁化率(-8.5×10-6),还有较高的维氏硬度(HV0.1=160)。     

Effect of compaction method on the structure and properties of bulk Cu + Cr<Subscript>3</Subscript>C<Subscript>2</Subscript> composites

Cu + Cr₃C₂ composites have been produced using the mechanical alloying of the elemental components, followed by severe plastic deformation by torsion, magnetic-pulse pressing, and electric-pulse plasma sintering. The composites are studied using X-ray diffraction and light and electron microscopy, as well as measurements of the hardness, density, and electric conductivity. Magnetic-pulse pressing at a temperature of 500°C makes it possible to produce volume nanocomposites with a homogeneous distribution of dispersed carbides over the copper matrix, which has a density of 96%, a Vickers microhardness of 4.6 GPa, a Rockwell hardness of 69 HRA, and an electric conductivity of 19% IACS units. Using electric-pulse plasma sintering at a temperature of 700°C, composites with the nanostructured copper matrix, which contains carbide inclusions and consists of domains surrounded by a layer of nearly pure copper, have been produced. These composites have a density of 88%, a Vickers microhardness of 4.0 GPa, a Rockwell hardness of 58 HRA, and electric conductivity of 26% IACS units.     

铅合金熔滴冲击45钢冷基板与45钢表面熔池的对比试验

针对特殊装备领域传统钢/铅粘接结构中存在的粘接层易老化脱落、长期稳定性差的问题，提出一种熔滴沉积复合TIG焊(gas tungsten arc welding)电弧增材制造新工艺，用于制造钢/铅双金属结构。文中比较性地研究了铅合金熔滴冲击铺展45钢冷基板与45钢表面熔池后的凝固形貌，通过引入无量纲数研究了熔滴冲击速度、温度对熔滴铺展凝固形貌的影响规律，利用OM，LSCM，SEM，EDS，XRD以及显微硬度测试等方法与手段，分析了熔滴沉积复合TIG电弧增材制造钢/铅双金属试样的界面微观组织结构与显微硬度。结果表明，铅合金堆积层铺展因子随熔滴冲击速度的增加呈明显非线性增加；界面层金属间化合物主要为FeSb2和FeSn2，其厚度随电弧热输入的增加而增加；钢/铅界面处的显微硬度明显高于铅合金堆积层和45钢母材；界面层中心左侧的硬度值达到最大值，为785.3 HV，45钢一侧平均硬度为343.7 HV，铅合金一侧平均硬度为24.3 HV。     

变极性等离子弧铝合金熔覆层组织和性能

采用变极性等离子弧熔覆技术在2219铝合金试板表面制备了熔覆层,用金相显微镜、扫描电子显微镜和能谱仪对熔覆层进行了显微组织形貌观察和元素分析,用显微硬度计对熔覆层显微硬度进行了测试.结果表明:熔覆层底部组织为垂直于熔合线方向生长的柱状晶,中上部为较细小的等轴晶;熔覆层在凝固过程中析出Q强化相;熔覆层具有较均匀的显微硬度.     

Effects of High Current Pulsed Electron Beam Irradiation on the Mechanical Properties and Cutting Performance of TiAlN-Coated Tools

Commercial TiAlN-coated carbide tools were post-treated using the high current pulsed electron beam irradiation method. The influence of the energy density of the electron beam on the morphology, phase composition, surface roughness and Vickers hardness were investigated. The higher energy density imposed on TiAlN-coated carbide tools resulted in a flatter and harder modified surface. After the beam irradiation, the XRD diffraction peak intensity of the hardening phase (Ti,Al)N was changed, and the diffraction peak position was shifted; these changes are attributed to the improved microhardness of the irradiated coatings. Investigations on the cutting experiments of turning Ti-6Al-4V alloy showed that the irradiated TiAlN-coated carbide tool exhibited longer cutting life and better wear resistance than those of an unirradiated tool. This improvement is attributed to the combined effect of low surface roughness and high microhardness that resulted from the high current pulse electron beam irradiation.     

Wear mechanism of AZ31 magnesium alloy irradiated by high-intensity pulsed ion beam

The wear resistance and wear mechanism of AZ31 magnesium alloy irradiated by high-intensity pulsed ion beam (HIPIB) at an ion current density of 100 A/cm² with shot number from one to ten are investigated by dry sliding wear tests. The cross-sectional microstructure and surface microhardness of the irradiated AZ31 magnesium alloys are examined by optical microscopy (OM) and Vickers tester, respectively. It is found that surface hardness increased with increasing shot number, from an original value of 570 MPa to a maximal value of 820 MPa with ten shots, and the wear rate of the samples irradiated with five and ten shots was about one order of magnitude less than that of the original sample. The transition from severe metallic wear to mild oxidative wear induced by HIPIB irradiation was identified through a combined analysis in surface morphology and chemical composition of wear tracks, mechanically mixed materials, wear debris and wear scars of counterface steel ball by using scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), which is mainly attributed to the significant increase in microhardness resulting from grain refinement on the irradiated surface.     

An application of universal hardness test to metal powder particles

Powder metallurgy is a “net shape” components producing technology from metal powders by compaction with following sintering processes. For today actual trends of powder metallurgy are associated with modern powder grades, alloyed by elements with high affinity to oxygen (Cr, Mn, Si, etc.). Contamination of powder particles by oxides and/or other secondary phases have a negative effect on their compressibility and sinterability. The geometry properties of powders give integral information about powder quality. Evaluation of yield strength and/or rather the strain hardening exponent, characterizing the mechanical properties on the level of individual particles, really is not possible. One of available approaches could be measurement of the microhardness of particles. The contribution deals with the evaluation of the microhardness of powder particles and specification of the factors affecting measured values. Using standard Vickers microhardness HV0.01 measurements for two different powders the results obtained showed large scattering from the average. This gave no possibility to identify the influence of alloying and particle matrix purity on microhardness. Problem was solved utilizing instrumented indentation test using NanoIndenter XP. This is usable technique for estimation of microhardness of powder particle matrix and gives possibility to recognize differences between different size fractions of particles. Based on the obtained results it was concluded, that absolute results of indentation hardness and indentation modulus are strongly affected by mounting resin type. Utilizing DSI method and mounting resin of proper hardness enabled to evaluate the microhardness of powders with different alloying element content. Influence of particles purity/size on powder microhardness was established as well. Indentation hardness and indentation modulus for sintered materials are in good agreement with the data for corresponding bulk materials. Obtained results confirm that universal hardness test is valuable instrument for evaluating of sintered materials properties.