To enhance the quality and wear-resistance of metal-based composite coatings, Ni62 composite coatings were prepared by laser cladding 65Mn surfaces with WC and TiC as reinforcing phase particles. The ...effects of the laser power and content of the reinforcing phase on the microstructure, element distribution, phase composition, microhardness, friction, and wear properties of the composite coatings were investigated. Focus was placed on the cracking and wear mechanisms of the coating. The metallurgical binding zone exhibited a serrated morphology. The growth patterns of the crystals of the cladding layer resulted in the formation of columnar, cytosolic, and dendrite (or equiaxed) crystals. The main physical phases of the composite coating were the solid-solution (Ni, Cr, Fe), CW3, and Ti composite phases. There were two primary cracks in the cladding layer, one penetrating from the coating to the substrate, and the other occurring mainly at the interface between the cladding layer and the substrate. CeO2 incorporation led to refinement of the cladding layer and a significant reduction in the surface and cross-sectional defects. Wear of the coating was mainly caused by the alternating effects of adhesive, delamination, and abrasive wear.
Fig. 7. SEM images of specimen cross-sections at different laser powers (a) 550 W specimen cross-sectional shape; (b) 600 W specimen cross-sectional shape; (c) 650 W specimen cross-sectional shape; (d) 700 W specimen cross-sectional shape.
As the power increased, the extent of the cladding zone and heat-affected zone increased and then decreased. The laser energy received per unit substrate area increased when the laser power increased. As a result, a relatively large and high-temperature melt pool was formed on the substrate, so a relatively more significant amount of mixed powder fell into the pool to form a larger cladding zone. Display omitted
•Laser cladding of WC + TiC reinforced particles showed a serrated morphological feature and formed an excellent metallurgical bond.•The intervention of CeO2 can refine the organization of the cladding layer.•The primary forms of wear of the coating were selective wear, delaminating wear, and alternating action of abrasive wear.
A thermomechanical simulator Gleeble 3800 was used to simulate the thermal cycles experienced by various heat-affected zones (HAZ) during the welding process. The influence of peak temperature (Tp, ...500°C–1320°C) on the hardness, microstructure, precipitates, and properties of complex steel 780FB with microalloyed elements Ti, Nb, and V was systematically studied. The contributions of dislocation strengthening, precipitation strengthening, fine grain strengthening, and phase transformation strengthening increments to strength changes of samples after different thermal cycles were quantified, and the calculated results were found to be consistent with the experimental data. Compared with 780FB, there was little change in microstructure and properties when Tp was 500°C. When Tp was 650°C, the increase in VC density from 43/µm2 to 288/µm2 caused the enhancement of hardness and strength. The precipitation strengthening increment (49.84 MPa) played a dominant role in strength improvement. As partial bainite in the microstructure of 780FB transformed into ferrite at Tp of 800°C, the weakening of phase transformation strengthening (−57.5 MPa) became the main factor in strength change. The softening and strength reduction further increased when Tp was up to 980°C, as 780FB completely recrystallized and transformed into ferrite and MA islands. The phase transformation strengthening further reduced by 74.75 MPa. When Tp was 1320°C, the VC density decreased from 43/µm2 to 13/µm2, and the (Ti,Nb)C density decreased from 34/µm2 to 14/µm2, leading to severe grain growth (2.24 µm to 19.89 µm) and bainite transformation. The decrease in precipitation strengthening (−26.86 MPa) and fine grain strengthening (−87.91 MPa) counteracted with the increase in phase transformation strengthening (51.62 MPa), resulting a slight decrease in hardness and strength.
A thermomechanical simulator Gleeble 3800 was used to simulate the thermal cycles experienced by various heat-affected zones (HAZ) during the welding process. The influence of peak temperature (Tp, ...500°C~1320°C) on the hardness, microstructure, precipitates, and properties of complex steel 780FB with microalloyed elements Ti, Nb, and V was systematically studied. The contributions of dislocation strengthening, precipitation strengthening, fine grain strengthening, and phase transformation strengthening increments to strength changes of samples after different thermal cycles were quantified, and the calculated results were found to be consistent with the experimental data. Compared with 780FB, there was little change in microstructure and properties when Tp was 500°C. When Tp was 650°C, the increase in VC density from 43/μm2 to 288/μm2 caused the enhancement of hardness and strength. The precipitation strengthening increment (49.84MPa) played a dominant role in strength improvement. As partial bainite in the microstructure of 780FB transformed into ferrite at Tp of 800°C, the weakening of phase transformation strengthening (-57.5MPa) became the main factor in strength change. The softening and strength reduction further increased when Tp was up to 980°C, as 780FB completely recrystallized and transformed into ferrite and MA islands. The phase transformation strengthening further reduced by 74.75MPa. When Tp was 1320°C, the VC density decreased from 43/μm2 to 13/μm2, and the (Ti,Nb)C density decreased from 34/μm2 to 14/μm2, leading to severe grain growth (2.24μm to 19.89μm) and bainite transformation. The decrease in precipitation strengthening (-26.86MPa) and fine grain strengthening (-87.91MPa) counteracted with the increase in phase transformation strengthening (51.62MPa), resulting a slight decrease in hardness and strength.
Compositional and microstructural heterogeneity are characteristics of modern multiphase steels. However, the quantitative characterization of these heterogeneities is rarely considered in scientific ...publications. We characterized the compositional and microstructural heterogeneity of a commercial complex-phase steel (CP800) by combining various electron microscopy techniques and nanoindentation. Compositional gradients of C and Mn were characterized qualitatively and quantitatively through electron probe microanalysis (EPMA). Electron backscatter diffraction (EBSD) results were utilized to identify and segment the microstructural constituents. A novel nanoindentation approach was used to obtain hardness maps. Cube-corner indenter and micro-newton load were applied to limit the indent depth and spacing between adjacent indents to the nanometer scale. A high-resolution hardness map was obtained and successfully overlapped with EPMA and EBSD results, based on which the correlation between compositional heterogeneity and hardness variation in complex-phase microstructure was successfully established.
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•By applying a novel nanoindentation technique, a hardness map with nanometer-scale resolution was obtained.•Correlative characterization method combining various electron microscopic techniques and nanoindentation was developed.•Results indicated the unneglected influence of Mn bands on local microstructure and hardness in the complex-phase steel.•Martensite introduced the severest hardness change regardless of the neighboring phases in the complex-phase steel.
This article discusses the fracture modelling accuracy of strain-driven ductile fracture models when introducing damage of high strength sheet steel. Numerical modelling of well-known fracture ...mechanical tests was conducted using a failure and damage model to control damage and fracture evolution. A thorough validation of the simulation results was conducted against results from laboratory testing. Such validations show that the damage and failure model is suited for modelling of material failure and fracture evolution of specimens without damage. However, pre-damaged specimens show less correlation as the damage and failure model over-predicts the displacement at crack initiation with an average of 28%. Consequently, the results in this article show the need for an extension of the damage and failure model that accounts for the fracture mechanisms at the crack tip. Such extension would aid in the improvement of fracture mechanical testing procedures and the modelling of high strength sheet metal manufacturing, as several sheet manufacturing processes are defined by material fracture.
This study explored how MoSi2-TaSi2 ratios in silicide alloys influence the oxygen resistance of ZrB2-MoSi2-TaSi2 coatings, using self-propagating high-temperature synthesis and spark plasma ...sintering. The oxidative self-separation effect of TaSi2 and MoSi2 enhances nanoscale Zr and Ta oxide particle dispersion, forming a Zr-B-Ta-Si-O glass with optimal oxygen-blocking in the 50ZrB2-(MoSi2-10TaSi2) coating (ZMT10). Compared to ZrB2-MoSi2, ZMT10 showed 28.87 % and 48.21 % reductions in weight gain and oxygen penetration, increasing protection to 99.71 %. Excessive TaSi2 leads to Ta5+ dissolution, oxide aggregation, and a dendritic structure, facilitating oxygen diffusion and oxidation, raising the oxygen penetration in 50ZrB2-(MoSi2-30TaSi2) to 0.73 %, lowering protection to 99.18 %.
•MoSi2-TaSi2 double silicide powders by SHS method to enhance the oxygen barrier of ZrB2 coatings.•Co-strengthening effect of MoSi2-TaSi2 double silicides reduced the oxidation activity of the coatings.•The low-content TaSi2 resulted in a 48.21 % reduction in oxygen permeability.•Diffusion of Zr/Ta oxides in glass films formed stable Zr-B-Ta-Si-O complex glass film.•Excessive addition of TaSi2 exacerbated oxide aggregation and formed a loose dendritic structure.
Complex-phase (CP) steels, with a multiphase microstructure, offer an excellent combination of high strength, ductility, and formability, making them an attractive alternative to conventional ...high-strength low-alloy (HSLA) steels in the automotive industry. However, the microstructure and fatigue property relation in CP steels is complex. This limits the full exploitation of CP steels in applications, such as heavy-vehicles, where excellent fatigue performance of thick-plates after punching holes is the critical parameter. In this work, we initiate the study of the relation between microstructure and fatigue properties of a commercial CP steel (800CP) and compare it with a conventional HSLA (500MC) steel. Fatigue property, tensile property, and fatigue crack growth rate (FCGR) testing are conducted and the performance of the two steels is rationalized using detailed microstructure characterization, before and after fatigue testing. FCGR testing shows that, despite a higher yield strength of the 800CP, both steels have a similar propagation rate due to a more tortuous crack propagation path and a higher quantity of secondary crack formation in the 800CP microstructure. The high cycle fatigue (HCF) testing shows that the fatigue limit in the 800CP is 25% higher. This increase in fatigue limit is attributed to the improved resistance to fatigue crack initiation in the 800CP due to its larger fraction of bainite.
We examine the effect of transformation sequence on the microstructure evolution and mechanical properties of complex phase steel consisting of bainite and martensite. Formation of martensite prior ...to bainite transformation provides uniform lath-type mixture of constituent phases, but preceding isothermal bainite transformation produces carbon-enriched blocky martensite embedded in the bainite. Even though the presence of carbon-enriched blocky martensite increases the strength of the alloy more effectively, the impact toughness is significantly deteriorated with a small fraction of martensite. On the other hand, uniform lath-type mixture of martensite and bainite provides moderate decreased or conserved impact toughness at martensite fraction up to 70%, which be considered as an exceedingly beneficial option to enhance the strength of complex phase steel without compromising impact toughness.
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Exact quadratic in momenta complex invariants are investigated for both time independent and time dependent one-dimensional Hamiltonian systems possessing higher order nonlinearities within the ...framework of the rationalization method. The extended complex phase space approach is utilized to map a real system into complex space. Such invariants are expected to play a role in the analysis of complex trajectories and help to understand some new phenomena associated with complex potentials.
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