Papers by Keyword: Vickers Hardness

Abstract: Barkhausen noise (BHN) is a technique that can be used to evaluate properties of ferromagnetic materials; case depth, coating depth, residual stress, grinding burnt damage, and hardness of a metallic material. The commercial BHN measuring devices commonly used are relatively expensive. Therefore, the steel industries in Thailand hardly use in their production process. A cost-effective measuring system based on BHN was developed in this research. The developed machine was tested by measuring the hardness of different steels. The hardness measured by the developed BHN system was validated with the hardness measured by the Vickers hardness test. It can be concluded that this proposed measuring machine can estimate the hardness of steels with accuracy of 96.76 percent on average (in hardness rage of 150 – 800 HV). This development can also be applied to measure other properties if the appropriate operating parameters of the machine are changed and calibrated with reliable standards.

Abstract: A 4Kg grade AlCoCrFeNi_2.2 high entropy alloy was prepared by low vacuum medium frequency induction melting. The microstructure results showed that the microstructure and composition of the ingot were uniform. The microstructures were composed of primary Ni-rich FCC phase and eutectic structure. The eutectic structure was composed of Ni-rich FCC phase and Al-rich B2 phase. The hardness results showed no significant difference in Vickers hardness between different parts of the ingot, and fluctuated within the range of HV260 ± 20. The compression test results showed that there was no significant difference in compression performance between different parts of the ingot. The AlCoCrFeNi_2.2 high entropy alloy had excellent compression performance, the yield strength reached 600 MPa, the fracture strength reached 2200 MPa, and the compression ratio was greater than 40%. Above all, the near-eutectic AlCoCrFeNi_2.2 high-entropy alloy had the characteristics of good casting ability, high strength, good plasticity, and was easy to realize the preparation of large-volume non-segregation ingot.

Abstract: The influence of various process parameters on the building of maraging steel powder by the selective laser melting (SLM) processes is investigated. The microstructure in the built part was observed and the influence of the heat treatment was evaluated. As results, the depth of solidified layer was higher than that of deposited metal powder, and its value was influenced with the process parameters. The microstructure in the boundary between the built part and the substrate was quite different from the built part even if the suitable heat treatment was performed.

Abstract: Titanium and its alloys possess high specific strength, excellent corrosion resistance and good biocompatibility [1] [2]. Since oxygen is an unavoidable impurity in such materials, it has been adopted as an alloying element in the development of low-cost titanium alloys. Therefore, it is important to investigate the role of oxygen in these alloys, especially in β-type alloys. In the present study, the effects of oxygen on the electrical resistivity, Vickers hardness and heat treatment behavior of a Ti-20mass%V alloy which is the lowest concentration for which the fully retained β phase is obtained were assessed. The electrical resistivity and Vickers hardness of solution-treated and quenched specimens increased with increasing oxygen content, due to the dissolution of oxygen into the β phase and solid solution hardening, respectively. Upon isothermal aging at 673 K, the addition of O accelerated a-phase precipitation. The addition of O was found to suppress the appearance of the athermal ω phase in the solution-treated and quenched state.

Abstract: Ti alloys are attractive materials for such applications, they are expensive due to the costly alloying elements such as Nb or Mo. The present authors have adopted Mn as a low-cost alloying element, and melted Ti-7, 7.5 and 8 mass%Mn-1.5 and 3mass%Al alloys using a laboratory-scale arc furnace. All specimens prepared from bottom ingots were heat treated at 1223 K for 3.6 ks and quenched in ice water. In the 7 and 7.5Mn-Al alloys, the β phase and orthorhombic martensite were identified using X-ray diffraction. In the 8Mn-Al alloys, only the β phase was identified. In the 7, 7.5, and 8Mn-Al alloys, the electrical resistivity at room and liquid nitrogen temperature increased with increasing Al content due to dissolution of Al into the β phase, whereas the Vickers hardness decreased with increasing Al content due to decreasing formation of athermal omega by the addition of Al. Heat treatment at 673 K for 60 s almost completely returned deformed Ti-7 and 7.5Mn-3Al specimens to their original shapes, and heat treatment at 773 K for 60 s almost returned deformed Ti-8Mn-Al specimens to their original shapes.

Abstract: Heat treatment is very important factor for improving material strength. In our previous work, we combined a furnace heating and induction heating to develop a new method (furnace-induction heating, FIH). We observed the microstructure in JIS SUJ2 bearing steel and found that FIH process refined the prior austenite grains. In this work, we further investigated the relation between hardness distribution and retained austenite in furnace-induction heated JIS SUJ2 steel.

Abstract: In order to solve the problem that the mechanical properties of containers and pipelines are difficult to evaluate during service, this paper focuses on the quantitative expression of hardness and mechanical properties. Taking the X70 pipeline steel as the research object, with 12 welds of the tensile test and 192 times the hardness of indentation test, the establishment of a mathematical application suitable for engineering applications. The results shows: The hardness, indentation parameters and mechanical properties of the weld, base metal and heat affected zone did not change significantly with the pipe wall thickness, it is reasonable to test the hardness of the outer wall of the pipeline at the scene; Vickers hardness distribution can effectively explain the fracture of the specimen, hardness and plastic work was inversely proportional.

Abstract: Long-term use of a denture base can be a reservoir of microbes due to porosities and mechanical wear of denture surfaces. Vanillin has an antimicrobial effect. However, its influence on physical properties after incorporated in PMMA has not yet been evaluated. The purpose of this study was to investigate physical properties of PMMA by incorporating vanillin in different concentrations. Material and method. There were three groups of PMMA with ten specimens per group. Flexural strength and flexural modulus were tested by using a 3-point bending machine, and surface hardness was determined by Vickers hardness test. One-way ANOVA and Kruskal Wallis tests were used to analyze all data at 0.05 significance level. Result. The 0.1% vanillin group yielded a significant difference in Vickers hardness number (17.15 HV) as compared to 0.5% vanillin group (16.30 HV) and without vanillin (15.30 HV). In contrast, the flexural strength and modulus showed no significant difference among test groups upon incorporation of vanillin. Conclusion. The vanillin incorporated PMMA group demonstrated higher surface hardness, compared to the group without vanillin. In addition, there were no significant differences in flexural strength and flexural modulus among the three groups. This study also found no adverse effect in physical properties of the vanillin incorporated PMMA.

Abstract: The technology of structure refinement in materials with the aim of achieving substantial mechanical properties and maintaining the required plasticity level is becoming increasingly useful in industrial practice. Magnesium alloys are very progressive materials for utilization in practice thanks to their high strength-to-weight ratios (tensile strength/density). The presented paper analyses the effect of the input heat treatment of the AZ31 alloy on the change of structure and strength properties through the process of severe plastic deformation (SPD), which finds an increasing utilization, especially in the automotive and aviation industry. For the study of the influence of the SPD process (ECAP method) on the properties of the AZ31 alloy, two types of thermal treatment of the initial state of the structure were selected. The analysis of the structure of the AZ31 alloy was performed in the initial state without heat treatment and subsequently after heat treatment. In the next part, the influence of the number of passes on the strengthening curves was evaluated. Mechanical properties of the AZ31 alloy after ECAP were evaluated by hardness measurement and completed by structure analysis.

Abstract: Due to the great effect of defects on the properties of the material including strength, ductility, resistivity and opacity, there are many techniques that are used in defect detecting. Positron annihilation spectroscopy (PAS), Vickers hardness, and X-ray diffraction were used to study the influence of plastic deformation on the properties of 8006 Al-alloy in this work. An increase in the positron lifetime and Vickers hardness with a bit Broadening of XRD peaks was observed with increasing the degree of deformation reflecting a large dislocation density produced by plastic deformation.