Journal of Materials Engineering and Performance最新文献

The motivation for this research was the need for a reliable prediction of the distribution of microstructural parameters in steels during thermomechanical processing. The stochastic model describing the evolution of dislocation populations and grain size, which considers the random phenomena occurring during the hot forming of metallic alloys, was extended by including phase transformations during cooling. Accounting for a stochastic character of the nucleation of the new phase is the main feature of the model. Steel was selected as an example of the metallic alloy and equations describing the nucleation probability were proposed for ferrite, pearlite and bainite. The accuracy and reliability of the model depends on the correctness of the determination of the coefficients corresponding to the specific material. In the present paper these coefficients were identified using the inverse analysis for the experimental data. Experiments composed constant cooling rate tests for cooling rates in the range 0.1-20 °C/s. The inverse approach to a nonlinear model is ill-conditioned and must be transferred into an optimization problem, which requires formulating the appropriate objective function. Since the model is stochastic, it was a crucial, yet demanding task. The objective function based on a metric of the distance between measured and calculated histograms was proposed to achieve this goal. The original stochastic approach to identifying the phase transformation model for steels was tested, and an appropriate optimization strategy was proposed.

Recently, the automotive industry has increasingly focused on additive manufacturing as a new technology for reducing the weights of automobiles. In this study, fatigue tests were conducted on additively manufactured high-entropy alloys with different defect characteristics to clarify the relationships between their defect characteristics and fatigue strengths and to elucidate their fatigue fracture mechanisms. In addition, the effect of shot peening as an effective fatigue strength improvement method for an additively manufactured component was investigated. As a result, when defects formed by additive manufacturing were smaller than crystal grains, the numbers and sizes of defects affect fatigue crack growth behavior and barely affect fatigue life. Shot peening reduces the crack growth rate and is effective in extending the fatigue life. However, improvement in the fatigue limit is not achieved because the crack initiation site is a facet. From the above results, for defects smaller than the grain size, shot peening is a more effective method for improving fatigue life than reducing the numbers and sizes of defects.

This paper uses a modified dynamic material modeling (MDMM) suggested by Murty and Rao to develop processing maps (PM) of 2205 duplex stainless steels (DSS). Gleeble 1500D, a thermo-mechanical simulator was used to conduct single hit compression tests at a temperature between 850 and 1050 °C and strain rates of 0.001-5 s⁻¹. Additionally hot compression tests at a strain rate of 15 s⁻¹ and same temperature range were also conducted on a Bahr 805 dilatometer. As per general procedure acquired stress-strain data were corrected for friction and adiabatic heating, before constructing PMs at true strains of 0.1, 0.3, 0.5 and 0.8. Microstructures to validate the PM were prepared from safe domains and instability regimes belonging to PM of 0.8 true strain. Results showed that hot processing at intermediate to high strain rates and temperature leads to formation of flow instabilities such as mechanical twins and adiabatic shear bands. Safe domain located within the temperature range of (850-925) °C, strain rates of (2.6-15) s⁻¹ and peak η = 35% gave an inhomogeneous microstructure with presumably non-uniform mechanical properties. This region was considered ideal for hot processing of 2205 DSS provided that deformation conditions are carefully controlled to optimise DRX. Low Z conditions also provided an optimum hot working for hot processing.

The fracture behavior of bi-material made of Ni-Cr-B-Si hardfacing alloy deposited over SS316LN substrate was evaluated under quasi-static and dynamic loads. The crack growth started from notch made on the deposit side and progress toward the substrate deposit interface under both loading conditions was monitored. The displacement rate in quasi-static loading and the loading rate for dynamic loading varied and crack propagation was studied. It was observed that the crack was deflected at the interface and not penetrated to the substrate, irrespective of loading conditions. The reason for crack deflection at the interface was analyzed using the energy-based method. It is shown that the ratio of fracture toughness of the interface to that of the substrate (0.044) is lower than the ratio of energy release rate for the deflecting crack to that of the penetrating crack (0.235). Thus, this material combination satisfies the condition for crack deflection rather than penetration. The fracture toughness of the interface was estimated as ~ 68 MPa m^1/2 and it falls between that of hardfacing alloy and SS316LN base metal. Optical and SEM examinations were conducted to corroborate the crack path deviations during crack growth. Results suggest that isolated cracks might be present on hardfaced coatings on critical components for which such cracks are usually not permitted. It may be allowed in preference to repair of these cracks, which is difficult and significantly increases the risk of additional cracks forming on the deposits because of the high susceptibility of the hardfacing alloy to cracking.

In this paper, laser surface texturing (LST) has been used to create the circular and diamond shape texturing pattern on martensitic steel of grade SS410 to alter the various mechanical, surface, and tribological properties. The mechanical and surface characterizations have done on various shape-textured surfaces on SS410. Moreover, the slurry jet erosion test has performed on textured surfaces using a slurry erosion test rig. The hardness value of the various textured shape surface is higher than the others because mechanism of material removal for pattern is melting and evaporation, after applying an intense heat sudden cooling takes place. This might be altering the microstructure and enhances the hardness of the textured steel. The hardness value was the highest for circular-inward-textured case (HV0.3≈206) among all texturing. The tensile and flexural yield strength has marginally increased after texturing. The value of percentage elongation has marginally decreased after texturing. The modulus values for all the textured samples have enhanced as compared to untextured sample. Moreover, the modulus value of diamond-in textured samples are observed to be the highest i.e., ≈265GPa. The contact angles for all shapes of texturing patterns have greater values than untextured samples. All the textured surfaces show the hydrophobic and untextured surface as hydrophilic behavior. The outward textured surface has greater contact angle value (≈110°) as compared to others. The erosion resistance for the untextured samples have lesser among all textured samples, and the circular-in pattern has the highest erosion resistance. Because the erosion resistance is primarily depend on the hardness of the material, the plowing, microcutting lips, crater, and carbide pull-out type of wear mechanism has been identified using a scanning electron microscope.

Aluminum alloys have gained widespread attention in various engineering sectors such as aerospace, automobile, and construction industries owing to their attractive properties. On the other hand, the tribological properties of aluminum alloys are of serious concern due to their limitation in terms of hardness. The objective of the current study was to enhance the surface mechanical properties including microhardness, compressive residual stress (CRS), and wear resistance of 7075-T651 aluminum alloy subjected to ultrasonic shot peening (USP). The samples of aluminum alloy were first treated with USP for various durations followed by different types of in-depth characterization. X-ray diffraction analysis was used to examine the bulk texture development after peening. The wear studies were carried out on a ball-on-plate wear testing machine under various applied loads. The results indicated an increase in hardness, surface roughness, and CRS of the samples with increasing USP time. Additionally, a marginal difference in the surface roughness of peened samples was observed for selected peening times. The wear depth and width of peened wear tracks were found to be less than those of un-peened ones. The surface tribological properties of the worn-out samples were studied using scanning electron microscopy (SEM). The elemental analysis was carried out using electron-dispersive spectroscopy (EDS).

Quenching and partitioning (Q&P) steels have emerged as highly promising contenders for automotive applications due to their exceptional blend of high strength and ductility, achieved through transformation-induced plasticity associated with retained austenite (RA). Hence, ensuring precise tailoring of RA content and morphology is crucial for Q&P steels. The present investigation aims to study the effect of quenching and partitioning times on RA stability, and the mechanical properties of 0.26C-1.87Mn-0.99Al-0.45Si steel subjected to hot rolling followed by direct quenching and partitioning (DQP). This present research introduces a new microstructural-based approach for identifying the optimal quenching and partitioning times to achieve a microstructure comprising of thin films of inter-lath austenite between martensite laths. DQP steels with longer quenching time exhibit blocky RA islands of smaller sizes. On the other hand, with a shorter quenching time, the microstructure contains a larger fraction of RA with higher carbon content, and this RA is predominantly film type along with small-sized blocky RA islands. This results in an excellent combination of mechanical properties (UTS of 1250 ± 39 MPa and % elongation to failure of 16%). The post-tensile microstructures were also examined using transmission electron microscopy, and film-type RA appears more resistant to strain-induced transformation.

Sanicro-25 is a high-temperature material used as the structural material for steam superheaters and reheaters in advanced ultra-supercritical power plants. The air oxidation behavior of Sanicro-25 with various surface roughnesses is being assessed at 650 °C for about 1000 h. Different surface-roughened samples were studied, namely polishing the sample up to diamond finish, grinding up to (80-grit finish and 600-grit finish) and grit blasted. The diamond finish sample showed more weight gain than others, and higher weight gain was observed in the initial oxidation stage. Attributed to different surface preparations leads to defects at different levels, which further alters the diffusion of various elements. The diamond finish sample showed the presence of Cr-rich oxides, and other samples showed the presence of Fe-rich oxides. Smooth surfaces promoted the formation of thick protective oxide scales.

Experiments using carbon fiber reinforcing nylon composite produced by fused deposition modeling were conducted to determine mechanical parameters such as impact strength, tensile strength, and flexural strength. Four parameters—layer thickness, printing speed, raster angle, infill density, and twenty-seven runs—were used in the Box–Behnken technique of experimental design. Carbon fiber–nylon composite materials have flexural strengths that range from 20.12 to 25.89 N/mm², tensile strengths that range from 22.75 to 34.35 N/mm², and impact strengths that range from 0.37 to 0.72 kJ/m². Tensile strength was significantly affected by printing speed, while impact and flexural strength was mainly influenced by layer thickness and raster angle. A scanning electron microscope was used on the broken sample to investigate the failure mechanism. Cavities, hillocks, smearing, fracture, ridges, pores, clusters, particle pullout, delamination, deep hole, protrusion, void, crack, infill gap, and interface all have an impact on composite fracture mechanisms.