Metal Science and Heat Treatment最新文献

We study the effect of duration of the exposure to hydrogen on the chemical compositions of the surface and inner layers of BB751P heat-resistant nickel alloy applied for manufacturing of the disks of aircraft engines. The samples were treated in a hydrogen atmosphere at 1473 K for 0, 15, 30 and 60 min. It is shown that the elemental composition and structure of the surface layer of the alloy change as the duration of holding in a hydrogen atmosphere increases. Moreover, the contents of oxygen, aluminum, titanium, chromium and niobium become many times higher, and we observe the formation of spherical nickel microparticles 0.5 – 3.0 μm in size. The composition of the internal layers of VV751P alloy varies insignificantly, which reveals the inhibition of the process of oxidation in the outer layer and the absence of penetration of the oxidation front into the alloy.

The metal-ceramic powdered composite castings of nickel-based powder reinforced with 10% SiC and 10% Al₂O₃ were successfully processed through in-situ melting via microwave hybrid heating route. The premixed powders of metal – x% ceramics were cast in graphite cavity under suscepting environment. The composites were developed within 15 – 20 minutes of 2.45 GHz microwaves exposure using domestic microwave applicator. Microstructure analysis of developed castings revealed uniform equiaxed grain growths of nickel based metallic powder matrix and uniform dispersed ceramic particles. Results revealed lower visible defects in cast samples and porosity was in the range of 1.25 – 1.28%. Microhardness studies revealed higher hardness of 1200 HV. The present work on in-situ powder melting and casting of composites provides an alternate energy efficient route for Metal Matrix composites processing.

This study investigates sintered magnets produced from alloys of a (Nd_0.75Dy_0.25)₃₂Fe_66.4–xCo_xCu_0.1Ga_0.6B_0.9 system with varying cobalt content. The Curie temperatures of the initial and sintered magnets were determined. A microstructural analysis and x-ray diffraction (XRD) of the magnets were carried out. We optimized the composition of the alloy and the two-stage annealing process. The alloy with an optimal composition of (Nd_0.75Dy_0.25)₃₂Fe_55.3Co_11.1Cu_0.1Ga_0.6B_0.9 (wt.%), prepared by a low-oxygen process, exhibited high hysteresis characteristics at room temperature (B_r = 11.72 kG; _MH_c = 20.8 kOe; _BH_c = 11.2 kOe; and (BH)_max = 32.9 MG ∙ Oe) and a reduced temperature coefficient of magnetic induction, α = |–0.053Ι| %/°C, in the range of 23 – 100°C. The formation of a nonmagnetic Laves phase (Nd, Dy)(Fe, Co, Cu, Ga)₂ along the grain boundaries was identified as the key factor contributing to the increase in coercive force (H_c) to 20.8 kOe. This enhancement was attributed to improved magnetic insulation between the grains of the main magnetic phase (Nd, Dy)₂(Fe, Co)₁₄B, resulting from the suppressed exchange interaction due to reduced magnetization of the (Nd, Dy)(Fe, Co, Cu, Ga)₂ phase, as the contents of gallium and copper increased.

This article examines the structure–phase state of Zr – 2.5Nb alloy subjected to prolonged low-temperature neutron irradiation in a water coolant using x-ray diffraction analysis and scanning electron microscopy (SEM), including electron backscattered diffraction (EBSD). The results demonstrate that zirconium hydrides with the γ(ZrH) and δ(ZrH_1.66) phases are formed both along grain boundaries and within the bulk of α(α′)-phase crystallites. These phases manifest as isolated plates, chains, or large clusters, depending on the initial microstructure and phase composition of the alloy. In all cases, specific orientation relationships are observed between the matrix α/α′/β phases and the hydride phases. A fracture analysis of welded Zr – 2.5Nb joints containing a high concentration of hydride phases revealed a brittle failure accompanied by characteristic cleavage facets.

We propose a method for monitoring the process of heat treatment of the cast components of freight cars including, in particular, large-sized side frames made of low-alloy steels. The necessity of development of a procedure of this kind is explained by the fact that, in numerous cases, it is impossible to establish the fact of realization of heat treatment after removing of the surface defects of side frames at the manufacturing plants with the help of electric-arc welding. This does not allow us to formalize the admission of frames to operation, which may lead to serious financial losses. Thus, in order to determine the presence and quality of heat treatment of side frames, we propose to use a method intended for monitoring of the welds by measuring the hardnesses of the base metal, weld metal, and the heat-affected zone. The influence of heat treatment on the microstructure and hardness of welded joints is investigated. The results of approval of the proposed method under the conditions of repair facility are presented.

The effect of reinforcement with carbon nanomaterials on the mechanical properties of AZ31 alloy (Mg – 3Al – 1Zn) obtained by powder metallurgy methods was studied. Hybrid reinforcement GNP/CNT was used to obtain composites. The weight fraction of CNT (carbon nanotubes) in the base alloy AZ31 was kept constant at 0.25 wt.%. The weight fraction of GNP (graphene nanoparticles) was changed, % (wt.): 0.75; 1.25; 1.75; 2.25. The surface morphology of the alloy was analyzed using scanning electron microscopy. Microhardness and compressive strength of the composites were experimentally determined. The results showed that reinforcement increases the mechanical properties of the AZ31 alloy.

This study examines the effect of diamond burnishing on the fatigue resistance and fracture mechanisms of drill pipes made of 2024 and 1953T1 aluminum alloys. Microstructural analysis, microhardness measurements, high-cycle fatigue testing, and fractographic examination were performed on specimens in the as-received and burnished conditions. Diamond burnishing increased the endurance limit of 1953T1 and 2024 alloys by 25% and 59%, respectively, due to surface hardening. After burnishing, the microhardness increased markedly from the pipe wall center to the surface, ranging from 150 – 156 HV and 166 – 172 HV in the center to 191 – 206 HV and 187 – 194 HV at the surface for 2024 and 1953T1 alloys, respectively. The surface hardening effect was significantly greater in naturally aged 2024 alloy than in artificially aged 1953T1 alloy.

A system of components containing three refractory elements, namely titanium, niobium, and zirconium, in combination with iron, chromium, and vanadium was studied for the purpose of manufacturing a cost-effective bio-high entropy alloy (HEA). The following three high-performance alloys were synthesized: TiZrNbCrV, TiZrNbFeCr, and TiZrNbFeV. The alloys were fabricated by employing a mechanical alloying method. The obtained powders were compacted at 2000 MPa and then sintered in argon and hydrogen atmosphere at 1150°C for 1 hour at a heating rate of 10 K/min. The structure and phase composition of the alloys were studied using an x-ray diffraction (XRD) analysis and field emission scanning electron microscopy (FE-SEM). The structure of all alloys included the following four regions: BCC phase (primary), HCP phase (small quantity), void space, and Nb (non-diffusion region).

The effect of 0.2 wt.% Ti modification on the microstructure, Brinell hardness and mechanical properties under static tension of ZG35 steel is studied. The morphological characteristics of the matrix phase and carbide were studied using an optical microscope. To determine the solubility of carbon in the solid solution by the degree of ferrite lattice distortion, the change in the ferrite lattice constant was measured by the XRD method. The grain size, dislocation density and the nature of their distribution in the matrix were determined by the EBSD method. It was found that effects of Ti on the structure and mechanical properties of cast ZG35 steel are complex, involving three adverse and one beneficial influence. At the same time, the strengthening effect of carbide was not revealed. The mechanism of titanium modification of cast steel is that the resulting TiC promotes grain refinement, increases the dislocation density in the microstructure and improves the deformation resistance of the matrix. This leads to an increase in the strength and hardness of the steel.

This study examines the structure and hardness of a layer (up to 9 mm thick) deposited by plasma transferred arc (PTA) surfacing of molybdenum high-speed steel (HSS) non-conducting cored wire onto 30KhGSA steel in a nitrogen atmosphere. A skeletal structure was observed in the deposited layer. A single high-temperature tempering of the surfacing sample with the substrate was shown to increase the microhardness of the deposited layer to 5.96 GPa, which is approximately twice the hardness of the substrate (30KhGSA steel). Microhardness remains nearly uniform across the surfacing thickness. Double tempering led to a further increase in the microhardness of the surface layer (100 μm thick) to 7.1 GPa. In this case, microhardness gradually decreases with depth, approaching values observed after single tempering. The formation of a hardened surface layer is attributed to its enrichment with carbon and oxygen atoms during surfacing, followed by the precipitation of oxycarbide particles during tempering.