The Effect of Vanadium Content Coupling with Heat Treatment Process on the Properties of Low-Vanadium Wear-Resistant Alloy

The development of wear-resistant materials with excellent properties is of great research value in the manufacturing industry. In this paper, a new kind of low-vanadium wear-resistant alloy was designed and characterized to unveil the influence of vanadium content coupling with heat treatment on the microstructure, hardness, and abrasive wear property. The performances of commercial high chromium cast iron (HCCI) and the new low-vanadium wear-resistant alloy are compared. The alloy with 3 wt.% vanadium quenched at 900 °C and tempered at 250 °C, possessing VC, Mo₂C, and M₇C₃ distributed in the martensite matrix, displayed a wear resistance two times better than the HCCI. The results showed that the increase of vanadium content from 0.98 wt.% to 3.00 wt.% resulted in a decrease in the size of M₇C₃ and a more homogeneous distribution of M₇C₃. VC with a bimodal distribution is effective for impeding grooving or indenting by abrasives because of their high hardness, which plays a vital role in improving the wear resistance of low-vanadium wear-resistant alloy.     

Investigation into Changes of Microstructure and Abrasive Wear Resistance Occurring in High Manganese Steel X120Mn12 during Isothermal Annealing and Re-Austenitisation Process

Hadfield steel, under unit pressure conditions, strengthens itself by forming a high density dislocation structure, which results in increased resistance to dynamic impact wear. However, under abrasion conditions, the homogeneous microstructure of the cast steel is insufficient to achieve the expected service life. The aim of the research is to conduct a comparative analysis of the material in its as-delivered state and after two-stage heat treatment (isothermal annealing followed by re-austenitisation). It was found that after isothermal annealing of X120Mn12 grade steel at a temperature of 510 °C, a microstructure with a complex morphology consisting of colonies of fine-grained pearlite, (Fe,Mn)₃C carbides distributed along the grain boundaries of the former austenite and needle-like (Fe,Mn)₃C carbides was obtained in the austenite matrix. The subsequent thermal treatment of the steel with the use of supersaturating annealing at 900 °C resulted in a heterogeneous microstructure consisting of evenly distributed globular carbide precipitations in a matrix of considerably finer austenite grains in comparison with the as-delivered original state. As a result of the final microstructural changes achieved, a 16.4% increase in abrasion resistance was obtained compared to the delivered condition.     

Microstructure and Corrosion Resistance of AZ91 Magnesium Alloy after Surface Remelting Treatment

The effect of surface remelting treatment on the microstructure and corrosion resistance of the AZ91 magnesium alloy was studied. The surface layer was remelted by GTAW (gas tungsten arc welding). An original two-burner system with welding torches operating in a tandem configuration was used, allowing the combination of cleaning the surface from oxides with the remelting process. The studies of the corrosion resistance of the alloy included electrochemical tests and measurements of the rate of hydrogen evolution. The results showed that surface remelting treatment leads to favorable microstructural changes, manifested in strong grain refinement and a more uniform arrangement of the β-Mg₁₇Al₁₂ phase. The changes in the microstructure caused by remelting and the accompanying fast crystallization contributed to an increase in the corrosion resistance of the remelted samples in comparison to their non-remelted equivalents. The results obtained on the basis of the polarization curves showed three-fold lower values of the corrosion current density in the case of the remelted material than the value of the corrosion current density determined for the starting material. In turn, in the case of measurements of the electrochemical noise and corrosion rate determined by the method of measuring the rate of hydrogen evolution, this value for the remelted alloy was two times lower. The research also showed that GTAW technology is highly effective and can be a valuable alternative to laser techniques. The complete experimental details, obtained results and their analyses are presented in this paper.     

Microstructure and Selected Properties of Iron–Vanadium Coatings Obtained by the Laser Processing of a VC Pre-Coat Applied on Steel—Single and Multiple Laser Tracks Study

This paper presents the results of the microstructure, mechanical and physicochemical properties of coatings produced by the remelting of a VC pre-coat applied in the form of a paste on 145Cr6 steel. The remelting process was carried out using a diode laser beam. A laser device with a rated power of 3 kW was used. During these tests, a constant laser beam scanning speed of 3 m/min was used. The variable parameter was the laser beam power. Values of 500 W, 900 W and 1100 W were used. In the first stage of this study, single laser tracks were formed, and basic tests, such as on microstructure, microhardness and chemical composition, were performed. In the second stage of this study, multiple laser tracks were prepared using previously selected parameters. On such specimens, it was possible to test the same traits as for single tracks and, additionally, to perform corrosion and wear resistance tests. It was found that the obtained coatings have different properties than the base material. No primary vanadium carbides were found in the melted zone, but the proposed production method contributed to an increase in microhardness and wear resistance.     

Microstructure and Wear Resistance of Laser Cladding of Fe-Based Alloy Coatings in Different Areas of Cladding Layer

In this study, laser cladding technology was used to prepare Fe-based alloy coating on a 27SiMn hydraulic support, and a turning treatment was used to obtain samples of the upper and middle regions of the cladding layer. The influence of microstructure, phase composition, hardness, and wear resistance in different areas of the cladding layer was studied through scanning electron microscopy (SEM), X-ray diffractometry (XRD), friction and wear tests, and microhardness. The results show that the bcc phase content in the upper region of the cladding layer is less than that in the middle region of the cladding layer, and the upper region of the cladding layer contains more metal compounds. The hardness of the middle region of the cladding layer is higher than that of the upper region of the cladding layer. At the same time, the main wear mechanism of the upper region of the cladding layer is adhesive wear and abrasive wear. The wear mechanism of the middle region of the cladding layer is mainly abrasive wear, with better wear resistance than the upper region of the cladding layer.     

The Effect of Quenching and Partitioning (Q&P) Heat Treatment on the Microstructure and Mechanical Properties of High Boron Steel

High boron steel is prone to brittle failure due to the boride distributed in it with net-like or fishbone morphology, which limit its applications. The Quenching and Partitioning (Q&P) heat treatment is a promising process to produce martensitic steel with excellent mechanical properties, especially high toughness by increasing the volume fraction of retained austensite (RA) in the martensitic matrix. In this work, the Q&P heat treatment is used to improve the inherent defect of insufficient toughness of high boron steel, and the effect mechanism of this process on microstructure transformation and the change of mechanical properties of the steel has also been investigated. The high boron steel as-casted is composed of martensite, retained austensite (RA) and eutectic borides. A proper quenching and partitioning heat treatment leads to a significant change of the microstructure and mechanical properties of the steel. The net-like and fishbone-like boride is partially broken and spheroidized. The volume fraction of RA increases from 10% in the as-cast condition to 19%, and its morphology also changes from blocky to film-like. Although the macro-hardness has slightly reduced, the toughness is significantly increased up to 7.5 J·cm⁻², and the wear resistance is also improved.     

Exfoliation Resistance,Microstructure, and Oxide Formation Mechanisms of the White Oxide Layer on CP Ti and Ti–Nb–Ta–Zr Alloys

We found that specific biomedical Ti and its alloys, such as CP Ti, Ti–29Nb–13Ta–4.6Zr, and Ti–36Nb–2Ta–3Zr–0.3O, form a bright white oxide layer after a particular oxidation heat treatment. In this paper, the interfacial microstructure of the oxide layer on Ti–29Nb–13Ta–4.6Zr and the exfoliation resistance of commercially pure (CP) Ti, Ti–29Nb–13Ta–4.6Zr, and Ti–36Nb–2Ta–3Zr–0.3O were investigated. The alloys investigated were oxidized at 1273 or 1323 K for 0.3–3.6 ks in an air furnace. The exfoliation stress of the oxide layer was high in Ti–29Nb–13Ta–4.6Zr and Ti–36Nb–2Ta–3Zr–0.3O, and the maximum exfoliation stress was as high as 70 MPa, which is almost the same as the stress exhibited by epoxy adhesives, whereas the exfoliation stress of the oxide layer on CP Ti was less than 7 MPa, regardless of duration time. The nanoindentation hardness and frictional coefficients of the oxide layer on Ti–29Nb–13Ta–4.6Zr suggested that the oxide layer was hard and robust enough for artificial tooth coating. The cross-sectional transmission electron microscopic observations of the microstructure of oxidized Ti–29Nb–13Ta–4.6Zr revealed that a continuous oxide layer formed on the surface of the alloys. The Au marker method revealed that both in- and out-diffusion occur during oxidation in Ti–29Nb–13Ta–4.6Zr and Ti–36Nb–2Ta–3Zr–0.3O, whereas only out-diffusion governs oxidation in CP Ti. The obtained results indicate that the high exfoliation resistance of the oxide layer on Ti–29Nb–13Ta–4.6Zr and Ti-36Nb-2Ta-3Zr-0.3O are attributed to their dense microstructures composing of fine particles, and a composition-graded interfacial microstructure. On the basis of the results of our microstructural observations, the oxide formation mechanism of the Ti–Nb–Ta–Zr alloy is discussed.