Papers by Keyword: Hardness

Abstract: Al is a active metal. However, it has a generally fine oxide film with thin and protective barrier, which is stable in air and neutral aqueous solution. Thus, Al alloys have been widely used in architectural trim, cold & hot-water storage vessels and piping. However, Al and most of their alloys may be easy to be corroded with various patterns of corrosion such as pitting, intergranular and galvanic corrosion etc. in the case of exposure to various industrial and marine corrosive environments. Therefore, an optimum evaluation of corrosion resistance for Al and Al alloys may be more important in a economical point of view. In this study, characteristics evaluation for ALDC 12 Al alloy by solution, normalizing, and aging (natural and artificial) heat treatments was carried out using electrochemical methods etc.. We can see that the hardness of ALDC 12 Al alloy were decreased by solution and aging heat treatments, in particular, the solution and natural aging (SNA) heat treatments indicated the lowest value of hardness. However, the lower hardness by heat treatment, the better corrosion resistance, for instance, the solution and natural aging (SNA) heat treatment exhibited the best corrosion resistance with showing the lowest hardness. Furthermore, the highest hardness was observed after normalizing and artificial aging (NAA) heat treatments. Therefore, it is considered that if improvement of the hardness as well as the corrosion resistance were to be required together, the normalizing and artificial aging (NAA) heat treatment should be performed. On the other hand, the solution and natural aging (SNA) heat treatment is thought to be an optimum heat treatment method for only corrosion resistance improvement.

Abstract: The intermetallic compound tin-copper (Cu-Sn) is widely used in the creation of high-quality bearings, electric conductive lubricants, 3D printers. However, when connecting two metals, the bond between atoms in the lattice becomes covalent or ionic. This leads to the fact that the material becomes more brittle. Additionally, the production of intermetallic compounds is cost-based in terms of both material resources and money. In this paper, the ceramics has been sintered based on the intermetallic copper-tin powders, obtained by plasma dynamic method. The raw powdered materials based on Cu-Sn were obtained using a coaxial magnetoplasma accelerator with copper electrodes by adding the crushed tin into the accelerator. Using X-ray diffractometry (XRD) and transmission electron microscopy (TEM) analyses, the presence of such phases as copper Cu and tin-copper Cu41Sn11 in the obtained material has been confirmed. Further, such-synthesized powdered products were used to obtain bulk samples using the spark plasma sintering technology at various sintering parameters. Images from scanning electron microscope showed a uniform sintering of the product at the sintering temperature of 440 °C under a pressure of 60 MPa. It was found that the sintered intermetallic ceramics has the Vickers hardness equal to 120 Hv. The obtained sample has the lower friction coefficient and the smaller wear area in comparison with the sample, made of pure copper.

Abstract: Treatment of hypereutectic structure silumin (18-24 wt% of Si) by an intense pulsed electron beam of submillisecond duration is carried out. Formation of submicro- and nanocrystalline structure in the surface layer is revealed, which is caused by ultrahigh (up to 10⁸ K/s) cooling rates of the melted layer. It is established that the modification of the silumin surface layer by an electron beam increases its hardness by 5 times.

Abstract: Production of A6063/SiC composite with various weight fractions (3%, 6%, 9%) were prepared by using permanent mould casting was investigated. The preferred mean particle size of SiC is 60 μm. In addition, A6063 alloys were cast for comparison purposes. The alloys and composites were given a T6 heat treatment process (solution treatment at 520 °C, water quenching at room temperature and artificial ageing at 180 °C), Also Microstructure, hardness and tensile properties of these composites were evaluated and compared. In addition, tribological properties of these composites were evaluated using a Pin-on-Disc apparatus with various parameters (constant load of 10N and varying velocities as follows 0.5m/s, 1m/s, 1.5m/s, 2m/s) .The microstructure of the composites shows homogenous distribution of SiC particles in the Al matrix except in the A6063/9% SiC composite. The wear and mechanical properties of composites improve with increasing the weight fraction of SiC Wear morphology studies show that higher wear rate in case of unreinforced specimen compared to heat treated composites. Whereas with the increase in SiC content, the material tends to fail in brittle mode. The aim of present study is to evaluate the effect of heat treatment on the mechanical and tribological properties of aluminum alloy A6063 /SiC metal matrix composite.

Abstract: The paper deals with microstructure characterization of a full-scale X14CrMoVNbN 10 1/ 27NiCrMoV 15-6 heterogeneous weld intended for IP/LP welded rotors. The welded rotors are being developed for modern turbines of coal fired power plants operating above 570 °C. The full–scale weld has been shown to be of good internal quality. Hardness surveys revealed the effects of post weld heat treatment parameters on weld metals and parent steels. Microstructure and precipitation of minor phases in parent materials, heat affected zones and weld metals in the state after the final stress relief annealing have been studied.

Abstract: The effect of the rare earth (RE) element Y on the microstructure and hardness of (Mg–0.5Zn–0.5Zr–2.8Nd –1.5Gd) wt% Mg alloy investigated. 1 wt. % Y was added and compared with the base alloy. The microstructure results show the refinement of the grain by the addition of Y and the grains became smaller about 31.8 % and the volume fraction was increases 11.1% %, which led to the increment of hardness from 48.33 HV (as-cast EV31A) to 53.71 HV (as-cast EV31A +1 Y). Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) results showed that the base alloy mainly contained α-Mg matrix and Mg-(Nd, Gd) as a second phase crystallized along the grain boundaries and addition of (Y) yttrium resulted in the formation of the new phase, Mg-Zn-Y-phase was found as a new ternary phase, where Y combined with the original second phase.

Abstract: This paper aim to investigate the effect on microstructure, hardness and wear (slurry erosion) of alloyed ductile iron (DI) with addition of 0.16% Chromium and 1.32% Nickel before and after boronizing process. The specimens were prepared by melting the Ductile Iron compositions through CO₂ sand casting method. Specimens were fully coated with boronizing paste and heated at 850°C and 900°C for 8 hours holding time. Microstructures of the specimens were observed under Olympus BX 41M Optical Microscope. Vickers Micro Hardness Tester was used to determine the hardness of the specimens while Wear Test (Slurry Erosion) to measure the wear volume of each specimen. After boronizing process, the boron element diffused into the specimens which make the surface harden. The thickest boride layer was detected at sample with temperature 900°C. The samples of 900°C give higher hardness than temperature 850°C which is 2909 HV and 1395 HV respectively. Referring to surface roughness test, samples boronized at 900oC had high wear resistance compared to sample boronized at 850oC and as cast. The selection temperature in boronizing treatment can prevent the rate of wear thus can identify the hardness of surface in order to prolong the equipment and application or even structure.

Abstract: Boronizing/boriding is a thermo mechanical process which produced protective surface layers to enhance the performance of engineering components utilized in mechanical, wear and corrosion. The present study investigate the microstructure and the hardness of boride layers formed on 0.28% Vanadium and 0.87% Nickel alloyed ductile iron after boronizing process. Specimens were boronized at 950° C for 6, 8 and 10 hours holding time before being cooled in the furnace. The microstructure and boride layer formed on the surface of substrates were observed under Olympus BX60 Optical Microscope. Vickers Micro Hardness Tester was also performed to determine the hardness of boride layers. Boride layer was formed by diffusion of the boron into the metal lattice at the surface which composed double phase of FeB and Fe₂B with saw-tooth morphology. The results of this study indicated that the thickness of boride layers increased from 109.8μm at 6 hours to 195.4μm at 8 hours holding time before they crack at 10 hours. The hardness of the material surface also increased from 1535 HV to 1623 HV at 6 and 8 hours respectively. In conclusion, the microstructure, borides thickness and hardness of borides layer were depending on boronizing time while temperature kept constant.

Abstract: In this study, the effects of various welding parameters on welding strength in low carbon steel JIS G 3101 SS400, welded by gas metal arc welding were investigated. Welding current, arc voltage and travel speed are the variable parameters were studied in this study. The ultimate tensile strength, hardness and heat affected zone were measured for each specimen after the welding operations, and the effects of these parameters on strength were examined. Then, the relationship between welding parameter and ultimate tensile strength, hardness and heat affected zone were determined. Based on the finding, the best parameter is formulated and used to calculate the heat input.

Abstract: The influence of holmium on the microstructure and hardness of Mg-Nd-Gd-Zn-Zr alloys were investigated. Conventional casting methods are used to produce the alloys. All the results were characterized by optical microscopy, scanning electron microscope (SEM) and the Vickers hardness test to highlight the influence of holmium addition. The addition of 2.0 wt.% holmium leads to the combination of rare earth elements which formed Mg-Zn-Nd-Ho phase. The results have shown the addition of Ho improved the microstructure and hardness of Mg-Nd-Gd-Zn-Zr alloys. By adding grain size of 2.0 wt.% holmium had reduced by 18.43%, while the volume fraction increased by 7.34%. The Vickers hardness value improved 6.18% due to the grain refine and volume fraction precipitates. The 2.0 wt.% holmium addition showed a positive result in microstructure and hardness value.