Papers by Keyword: Hardness

Abstract: Applications of advanced heat resistant ferritic steels in boiler repairs require detailed information on the creep behaviour of welds made of various combinations of steels. The paper deals with the results of hardness and microstructure characterization of a dissimilar circumferential weld of 14MoV6-3 and P91 tubes after about 10 years of service exposure in a boiler operated at 580 °C and steam pressure of 10.3 MPa. The P91 tube (f38x4 mm) was welded to the 14MoV6-3 tube (f38x6.3 mm) using the GTAW (141) technology. Bőhler-FOX IN 9-IG (3Cr0.5Mo0.3V) wires were applied as a filler material. Microhardness evaluation after long-term service exposure revealed two carburized zones, values in these zones did not exceed 350 HV0.5. The slowdown of recrystallization in partially decarburized areas of the 14MoV6-3 and the WM suppressed the formation of soft ferritic bands along fusion lines. This phenomenon is related to the high thermodynamic stability of V(C,N) particles in vanadium-bearing low alloy heat resistant ferritic steels at temperatures below 600 °C.

Abstract: The aim of the study was to prepare samples suitable for testing the shape memory phenomenon in ceramic systems. Testing would be carried out by preparing micro-objects with dimensions in the order of micrometers using SEM/FIB techniques, and subsequent testing using a nanoindenter. The article deals with the influence of the preparation method on the properties of samples prepared by conventional annealing and spark plasma sintering. Two commercial powders were used, namely PSZ-10C and PSZ-20C. The microstructure of the samples, fracture surfaces and HV hardness, as well as indentation hardness were evaluated on the prepared samples. It was shown, that both conventional annealing and SPS can be used for preparation of samples with a suitable grain size, but also that the preparation method has a significant impact on the properties of the sample. Depending on the preparation method, the grain size varied from approximately 1 μm to 50 μm. There is also difference in the character of the fracture surfaces and in the hardness of the samples, where a difference in indentation hardness from approximately 10 GPa to approximately 20 GPa was measured.

Abstract: The paper presents a new concept of a thermally sprayed composite coating obtained by mixing NiCrAl powder with chromium carbide Cr₃C₂ in an amount of approximately 30 wt.%. The aim of the research was to obtain a material combining the advantages of a metallic matrix and a ceramic phase, with increased resistance to wear and erosion. The plasma spraying (APS) process was carried out on a carbon steel substrate with variable technological parameters: arc current intensity (300/500/700 A) and hydrogen flow (4/8/12 NLPM), while maintaining the other conditions constant.The thickness, porosity, microstructure, chemical composition (using the EDS method), hardness, erosion resistance, and tribological wear of the coatings were evaluated. The results showed that the greatest thickness (approx. 150 µm) and lowest porosity (below 3 vol. %) were obtained at the maximum process parameters – 700 A and 12 NLPM. In turn, the thinnest and most irregular coating (approx. 70 µm) was obtained at the lowest hydrogen flow (4 NLPM), which was due to insufficient melting of the powder particles.Increasing the current intensity and hydrogen flow had a beneficial effect on all analyzed coating properties – especially hardness (up to 273.7 HV0.2), erosion resistance (the smallest mass loss of 0.007 g), and tribological wear resistance (the smallest volume loss of 2.925 mm³). A decrease in any of the parameters resulted in a deterioration of the layer properties. The optimal mechanical and structural properties of the NiCrAl + Cr₃C₂ composite coating were achieved at the maximum plasma spraying parameters: a power current of 700 A and a hydrogen flow rate of 12 NLPM.

Abstract: The increasing demand for Al7075 metal matrix composites (MMCs) stems from their exceptional characteristics, which include a high strength-to-weight ratio, low density, and superior mechanical characteristics. This research focuses on strengthening the Al7075 aluminum alloy by incorporating silicon carbide (SiC) and graphite particles. The material was produced through stir casting, using constant weight proportions of 3% SiC and 7% graphite. The research investigates the machinability of the stir-casting fabricated Al7075-SiC-Gr composites through turning operations under dry cutting conditions. Key process parameters include cutting speed (520, 840, 1200 RPM), axial feed rate (0.15, 0.25, 0.35 mm/rev), and doc (0.1, 0.2, 0.3 mm) were varied to assess their impact on power consumption. Results indicate that power consumption rises with increased cutting speed and doc. Among the factors, machining speed significantly affects power consumption, contributing 2.74% to the increase in power usage. This study highlights the vital role of machining parameters in optimizing the performance of Al7075-SiC-Gr MMCs and provides insights for enhancing both efficiency and surface quality in manufacturing applications.

Abstract: The automotive industry has been challenged by the rising need for lighter, environmentally friendly, low-emission, and low-energy consumption vehicles. Aluminium is regarded as a viable alternative to the heavier materials presently used in manufacturing automobiles due to its desirable characteristics. A review of the application of hybrid aluminium matrix composites (HAMCs) and aluminium matrix composites (AMCs) in the automotive sector is discussed in this paper. An overview of the properties and applications of fiber-reinforced, discontinuous, and particle-reinforced AMCs and HAMCs is given. Due to their superior mechanical, tribological, and physical properties, aluminium composite materials have emerged as the material of choice for most engineering applications. A discussion of the importance of proper selection of materials is also presented. The potential applications of AMCs and HAMCs in the automotive industry, i.e., brake discs and drums, cylinder blocks and liners, pistons, crankshafts, connecting rods, brake calipers, turbo heat exchangers, and others, are also addressed in this review. Recent trends and trends forming in aluminium use in automotive applications are also determined through the assessment.

Abstract: Aim: This research evaluates the strength and stability of hemp, kenaf, and coir fiber reinforced composites produced by compression molding for industrial applications. Materials and Methods: Hemp, kenaf, and coir fibers are blended with a polymer matrix and compression molded. Group 1 (Traditional) This article illustrates the effective fabrication of hybrid fiber. Ultimately stabilized to a medium percentage of resin (75%). Group 2 (Composite) hemp, kenaf & coir blended fiber source more tensile, compressive strength and minimum water absorption rate and wear behavior. Result: The best were the kenaf composites, then hemp water resistance, and they all possessed good thermal stability. Compression molding assisted in enhancing fiber bonding. Conclusion: Compression molding improved the adhesion of fiber and matrix. Kenaf composite exhibited maximum strength, hemp exhibited maximum water resistance, and all of them exhibited good thermal stability.

Abstract: Lightweight steel structural systems like trusses or built-up beams, made of thin gage steel elements, are highly efficient, with ease of handling and construction. Self-drilling screws are commonly used for connecting thin-walled elements, but the time and manpower required for numerous connections necessitate an improved solution. One possible solution is to use welding technology, but the conventional methods are not suitable for joining thin sheets. Manufacturing defect-free, mechanically sound welding joints remains challenging due to defects like porosity and undesired microstructural phases in the heat-affected (HAZ) and fusion zones (FZ). Conventional welding processes increase heat input, causing difficult challenges. Brazing, a relatively new joining process, offers the advantages of lower heat input for thin and zinc-coated steel sheets. Therefore, the paper aims to present the effect of MIG brazing parameters on the macro-and microstructural properties of Cu-Al-based weld seams manufactured for joining thin sheets with thickens in the range of 0.8-2 mm. The weld seams were manually fabricated using a MEGAPULS FOCUS 330 compact equipped with TBI XP 363S/4m welding torch, focusing on optimal welding regimes. The macro-and microstructures of the joints were evaluated along with the mechanical properties in terms of hardness, confirming that MIG brazing is a promising method for manufacturing lightweight steel structural systems.

Abstract: The mechanical properties of anodic oxide films of Nb, Ta and Zr were studied by the nanoindentation method. Anomalously high elastic recovery after deformation was observed for oxides with thickness of 20 nm. An analogue of this behavior can be elastic membrane fixed on soft base that does not prevent the membrane from bending. Increase of the oxide thickness to 300 nm reduced the effect associated with the high elasticity of oxide and easy deformation of the soft metal substrate, and was accompanied by an increase in the plastic component of deformation, which is similar to the behavior of ceramic materials with low elastic and significant residual plastic deformation.

Abstract: The present work includes an investigation of the effect of α-alumina nanoparticles addition to aluminum-based nanocomposites on its mechanical properties and finding the optimal value of alumina nanoparticles that give the best properties. Experimental work includes manufacturing samples of aluminum-based nanocomposite reinforced with alumina nanoparticles by powder metallurgy- hot forging process. Mechanical properties were tested. The results show an increase in hardness and compression yield strength with increasing the weight percentage of alumina nanoparticles, while the wear rate decreased to certain percentages of addition and then increased again. From the experimental results, multiple regression analysis methods have been used to obtain an empirical equation for predicting the mechanical properties and describe the behavior of hardness, compression strength, and wear rate. Genetic Algorithm Optimization was applied to find the optimum value of alumina nanoparticles weight percentage which gives good mechanical properties.

Abstract: The efficiency, precision, and expected lifespan of mechanisms and machine components (such as ball bearings, couplings, and gauges) are significantly influenced by the quality of the materials used. Thus, it is essential to select materials that offer well-defined hardness and stability throughout the product's lifetime. This paper examines the heat treatment applied to 100Cr6 steel to achieve precise hardness in the range of 230–390 HV10, while also meeting requirements for stability and uniformity over the product's lifespan.