Papers by Keyword: Hardness

Abstract: A non-Equi atomic W₂₄Ta₂₄Nb₂₄Cr₁₆Al₁₂ high entropy alloy (HEA) was designed based on thermodynamic calculations in order to obtain a single body-centered cubic (BCC) structure. The HEA was further fabricated by using the vacuum arc melting technique. The structural analysis of the HEA revealed the formation of a single BCC phase with the lattice parameter of 3.259Å. The micrograph of the HEA revealed dendritic structure with inter-dendritic segregations. The thermal analysis confirmed that the HEA is quite stable at high temperatures up to 1600°C. The thermal expansion of the HEA was also very low at 1100°C. The mechanical property such as the hardness of the HEA at room temperature, was quite high at 467 ± 20 HV₀.₅. The HEA was further heat treated at a very high temperature (1000°C) and the structural and mechanical properties were evaluated. The heat-treated HEA shows excellent structural stability as no secondary phases were formed in those samples. The mechanical property such as hardness of the HEA was increased continuously on increasing the heat treatment duration, which shows that the current alloy is highly preferable for possible high-temperature applications.

Abstract: The healing of bone defects is still challenging as therapies like autografts and allografts have limited benefits, especially in load-bearing positions. Bovine Hydroxyapatite (BHA) is a natural biological substance that can be used as a filler to replace damaged bones and overcome the low fracture toughness and brittleness of synthetic Hydroxyapatite (HA). This study presents the precipitation method of Magnesium (Mg)-doped Bovine Hydroxyapatite (Mg-BHA). FTIR analysis ensured the existence of phosphate (PO₄ ³), hydroxyl (OH) and carbonate (CO ^-2) groups of HA. After sintering, XRD analysis showed excellent stability in the BHA structure, represented by a slight change in Mg position. Vickers hardness showed a massive increment from ~4.6 GPa to ~7 GPa as the impurity rate increased. SEM analysis showed a denser microstructure with less porosity as the amount of Mg concentration increased. This research ensured that MgBHA could be potentially applied for medical applications due to the improvement in physical and mechanical properties of HA.

Abstract: To investigate creep rupture properties and microstructural changes due to creep of the Mod.9Cr-1Mo steel with high initial hardness, creep rupture tests were carried out at 600°C and 650°C. The hardness of the gauge and grip portions of the ruptured specimens were also measured. This steel exhibited higher creep rupture strength than the conventional material at the two temperatures, but its creep rupture strength showed a larger decreasing tendency at 650°C. For the specimens ruptured at 600°C, an increasing tendency in lath width and a decreasing one in hardness were confirmed in gauge portions, but they were not observed in grip portions. However, for the specimens ruptured at 650°C, the hardness of both gauge and grip portions tended to decrease with the time to rupture, and the recovery of the lath structure and the coarsening of M₂₃C₆ carbides were particularly noticeable in the gauge portions.

Abstract: Incremental sheet forming is a viable method for manufacturing highly customized components from non-conventional materials. Among these, niobium is a metal of growing interest due to its potential in various technological applications. In this experimental study, the incremental forming of high-purity annealed niobium sheets was investigated, with particular attention given to the surface finish of the formed parts. To this end, the surface morphology of the components, specifically fixed wall conical frusta, and the forming forces were analyzed. The results indicate that, despite the material’s notable formability, the incrementally formed niobium surfaces exhibit poor quality. This is attributed to the unique properties of niobium, suggesting that the development of surface treatment strategies is advisable to improve this aspect.

Abstract: This study investigates the effect of induction-based surface heat treatment on the microstructure and bendability of a commercial hot-rolled martensitic steel with a nominal strength of 1300 MPa. A rapid tempering process was applied at 500 °C and 700 °C using a pilot-scale 60 kW induction heating system, followed by water quenching. Microstructural characterization revealed that the treatment induced minor changes near the subsurface without affecting the centerline. The as-rolled condition exhibited the highest subsurface hardness, whereas surface-treated samples showed progressive softening due to recovery. Three-point bending tests combined with digital image correlation demonstrated a significant improvement in bendability for heat-treated samples. The as-rolled condition fractured at 0.195 strain, while the 700 °C treated specimen did not fracture even at 0.78 strain. These findings highlight that even a modest reduction in subsurface hardness can substantially enhance the formability of ultra-high-strength steels, offering a promising approach for industrial applications requiring high strength and improved bendability.

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.