Papers by Keyword: Heat Treatment

Abstract: This study assesses the impact of heat treatment on the microstructure and mechanical properties of AlSi10Mg alloy produced using the L-PBF method. The research compares the mechanical properties and microstructure of samples subjected to direct aging (heat treatment at 170 °C/2 h) and stress relief annealing (at 240 °C/2 h), which is below the temperature for silicon network decomposition. These results are then compared with the as-built state (without any heat treatment) after printing, serving as a reference. Tensile and hardness tests were used to determine the mechanical properties, while electron microscopy was employed to analyze the microstructure. The findings indicate that direct aging led to an increase in yield strength, tensile strength and hardness compared to the as-built state. In contrast, samples treated with stress-relief annealing exhibited comparable yield strength to the as-built state, but significantly lower tensile strength and reduced hardness. Notably, contrary to expectations, the ductility did not increase with decreasing strength and hardness; instead, it decreased.

Abstract: The 8-inch silicon carbide crystals prepared by physical vapor transport (PVT) offer a low-cost pathway for chip production, significantly enhancing the economies of scale. However, point defects， such as vacancies, interstitial atoms, and dislocated atoms produced by the temperature gradient mismatch and the fluctuation of the C/Si ratio during the growth process, seriously affect the residual stresses and the crystalline quality of the crystals. Using stress birefringence optical path difference and X-ray diffraction rocking curve detection methods, we characterized crystals annealed at different temperature. It is well-known that the residual stress of the wafer exhibits an uneven distribution, with the residual stress at the edge of the wafer significantly higher than that at the center. When the post-growth annealing temperature is below 2000°C, the residual stress of the crystal decreases rapidly due to the annihilation and transformation of point defects. However, when the temperature is increased further to 2200°C, a large number of irreparable and large-sized point defect clusters form, which severely degrade the crystalline quality of the crystal, induces lattice distortion, and lead to the generation of residual stress. Overall, the best residual stress relief is achieved at a post-growth annealing temperature of 2000°C.

Abstract: Ballistic steels are used for the basic ballistic protection of armoured vehicles against the compressive energy of exploding munitions and the impact energy of projectiles fired from small arms. Steels with hardness up to 500 HBW are used to protect the chassis of armoured vehicles. Steels with a hardness greater than 500 HBW are used to protect the cabs and turrets of armoured vehicles. Ballistic steels belong to the class of low alloy high strength steels where a good combination of high strength and toughness is required. Higher strength is achieved in the final production process which involves heat treatment by quenching and tempering. This treatment creates a martensitic structure. Another heat treatment option is the Q-P (quenching and partitioning) process, where higher material strengths can be achieved in some steels while maintaining ductility. This paper focuses on a comparison of the microstructure as observed using a light microscope of the ballistic steel Secure after heat treatment by the manufacturer and after heat treatment by the Q-P process. It was found that the Q-P process produces a finer grained structure and a change in mechanical properties due to the stabilised austenite and strained martensite in the microstructure of the ballistic steel.

Abstract: The article deals with the influence of process parameters on the properties of the protective coating deposited by Cold Spray technology on X52 pipeline steel. Part of the work is the evaluation of the effect of heat treatment on the resulting properties of the coating. Diamalloy 1003 powder was deposited on X52 steel substrate using four different process parameters, and then the samples were heat treated at 600°C, 800°C and 1000°C. The evaluation of results included analysis of microstructure, porosity and microhardness. The results show that heat treatment has a significant effect on the properties of the coating. The lowest porosity values for all tested parameters were achieved after heat treatment of 1000°C/1 hour.

Abstract: The article considers the features of heat treatment of steels, includes quenching, phase transformations and their influence on the structure and properties of the material. The key parameters of heat treatment are described: heating temperature, holding time and cooling rate, as well as their role in forming the required mechanical characteristics of steel. Phase diagrams are considered, in particular for the "iron-carbon" system, and their significance for choosing processing modes. Additional friction-strain hardening (AFSH) of various steel grades (20, 45, U7, U12) after preliminary quenching and low-temperature tempering is studied. An analysis of microstructural changes and microhardness of surface layers after AFSH is carried out, which confirmed the effectiveness of additional hardening. It was found that steels with a higher carbon content, limited to 0.8 %, demonstrate a greater depth of the hardened layer and higher microhardness values, which determines their feasibility for use in conditions of increased wear. The results of the study emphasize the importance of choosing the optimal AFSH mode depending on the carbon content in the steel, which has a significant impact on the formation of the strength characteristics of the material.

Abstract: A computer program in Python was developed based on the mathematical model, which allows obtaining preliminary calculations of the diffusion coefficient and nitriding time of a punch part. As a result of a numerical experiment, the process of nitrogen diffusion into the depth of the part was studied. The redistribution of nitrogen occurs as a result of diffusion due to the nitrogen concentration gradient in the volume of the part and the high quenching temperature. The numerical experiment confirms the full-scale experiment. Nitrogen penetration into the depth of the metal occurs precisely at the quenching temperature. The nitrogen content in the internal nitriding zone due to the nitrogen released from the surface layer increases and decreases on the surface with the exposure time of the part. Computer modeling and research of the diffusion coefficient in the process of heat treatment after ion nitriding made it possible to establish that for tool steels, diffusion along grain boundaries occurs. Thus, the use of complex ion nitriding (CIN), i.e. ion nitriding and subsequent heat treatment of nitrided parts allows you to change the phase composition and increase the depth of the nitrided layer due to nitrogen doping, control the nitrogen concentration and hardness along the depth of the nitrided layer due to selected modes.

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.

Abstract: Titanium is the material of choice for high performances components, due to the combination of physical and mechanical properties it provides and is widely used in aerospace, automotive, biomedical and marine engineering due to their good hot and cold processing properties, fracture toughness, high specific strength and good deformability. Nevertheless, titanium is also characterized by very high production costs, which are approximately 6 times and 30 times higher, respectively, in comparison to those to obtain the same quantity of aluminum or steel relegating titanium to high demanding sectors. One possible way to reduce the cost of titanium is to use cheaper alloying elements instead of vanadium or niobium to stabilize the body-centered-cubic (B.C.C) β-phase. TIG-welding of high-strength low-cost pseudo-β titanium alloys is complicated, primarily due to the high content of alloying elements, such as iron, molybdenum, as well as the use of oxygen as an alloying elements. By the correct choice of welding modes in most cases, it is possible to obtain welded joints of high-strength pseudo-β titanium alloys with good microstructure and mechanical properties. In this article, we study the weldability and influence of TIG welding on the structure and mechanical properties of low-cost titanium alloy Ti–2.8Al–5.1Mo–4.9Fe.

Abstract: A study of the mechanical properties of hybrid additive manufactured IN718 components is presented, optimising mechanical properties due to an in-situ high-speed milling and different heat treatment processes. At first, the impact of different heat treatment processes is investigated, as the changes in microstructure during the process lead to different mechanical properties. Static and dynamic mechanical load behaviour is tested, quantifying microstructural changes by means of the Ultimate Tensile Strength (UTS) and the endurance limit. Furthermore, sole PBF-LB/M- and hybrid built components are compared, investigating the effect of a surface finish on the static and dynamic load behaviour, as superficial cracks and melting errors diminish the UTS and the endurance limit of PBF-LB/M-built components. Within these experiments, a change of fatigue behaviour for the heat-treatedstates can be observed, compared to the as-built state of the PBF-LB/M, as the development of different phases during heat treatment leads to an improvement of the endurance limit for, e.g., solution and ageing treated components. Additionally, the improvement of the surface quality to Ra = 2 µm leads to a significant increase of the dynamic mechanical load behaviour of hybrid-built components, as superficial cracks and surface defects are reduced.

Abstract: Controlling nanomaterials' morphology and molecular structures offers many advantages, such as tunable material properties, lightweight, and high surface-to-volume ratio. Studies have focused on electrospinning as one of the most effective methods in fabricating nanofibrous materials and have closely considered various post-fabrication techniques to improve mechanical properties. This work investigates the effect of constrained heating at 100°C, 110°C and 120°C on the morphology, the static and dynamic mechanical properties, and crystallization properties of electrospun Poly(vinyl) alcohol (PVA) nanofibrous membranes. Constrained heating of PVA nanofibrous membranes at 120°C has the best overall improvement. As compared to unheated samples, the Young’s modulus is multiplied by more than 3, the tensile strength increases more than 75%. At the same time, the fiber diameter decreases from 282.4 nm to 222.2 nm, and the degree of crystallinity and crystallite size increases by more than 10% and about 75%, respectively. This change in molecular structure and the increase in mechanical properties suggest that constrained heating should be further explored to diversify load bearing applications.