CrN, CrTiN, CrAlN and CrTiAlN coatings were deposited on Si (100) wafers, and their microstructure, mechanical properties, fracture toughness and adhesive strength were investigated via X-ray ...diffraction (XRD), nanoindentation and micro-scratch tests. Besides an F.C.C. crystal structure, TiN0.3 (004) and AlN (222) phases were found in the CrTiN and CrAlN coatings while the crystallinity of the CrTiAlN coating decreased. The hardness of the CrN (14.5GPa), CrTiN (13.9GPa) and CrAlN (17.7GPa) coatings was determined by their grain sizes while the CrTiAlN coating with the most compact morphology exhibited the highest hardness of 22.0GPa. In addition, CrTiN (KIc=2.73MPa·m), CrAlN (KIc=2.70MPa·m) and CrTiAlN coatings showed a stronger crack resistance than the CrN coating (KIc=1.06MPa·m), especially the CrTiAlN coating without any radial cracks. However, the CrTiAlN coating encountered circumferential cracks and premature delamination (Adhesive energy Gc=70J/m2) because of its highest compressive stress (4.64GPa). Based on the results here, it is concluded that a decent compressive stress of 3.0GPa is expected to help thin films prevent from radial and circumferential cracks simultaneously.
Fig. 1 Different categories of cracks and corresponding load–unload curves for (a) CrN (b) CrTiN (c) CrAlN (d) CrTiAlN coatings under 1000mN nanoindentation Display omitted
•CrTiAlN presented the highest hardness as well as compressive stress.•CrTiAlN completely prevented from radial cracks under 1000mN nanoindentation.•CrTiAlN coating confronted circumferential cracks due to high compressive stress.•Difference of compressive stress and load pressure led to pop-out during unloading.•A compressive stress of 3.0GPa helps avoid radial and circumferential cracks.
The influence of a pre-deformation mode during the thermomechanical treatment of an A2139 Al alloy plate on the non-homogeneity of plastic deformation and mechanical properties was investigated. Two ...pre-deformation modes were selected: cold stretching (CS) and cold rolling (CR). The CS mode demonstrated a uniform equivalent strain in the thickness direction. However, a higher overall equivalent strain was observed in the CR mode, with the equivalent strain being higher on the surface than at the center of the plate. When a pre-deformation of 7% was applied, surface defects, such as orange peels, occurred on the plate surface in the CS mode. In contrast, in the CR mode, a clean surface was obtained. Therefore, to obtain a clean plate surface, pre-deformation through CR is more effective than that through CS. With the application of pre-deformation, hardness and strength increased significantly without a decrease in elongation, and the time required to reach peak aging could be shortened significantly. The CR mode exhibited greater improvements in terms of hardness and strength compared to the CS mode. However, in terms of toughness, the CS mode showed a greater improvement than the CR mode. Therefore, to achieve both high strength and a clean plate surface with increasing pre-deformation, utilizing the CR mode is more effective. In the CR mode, despite a significant reduction in the residual stress after artificial aging, a weak tensile residual stress remained on the surface. By contrast, in the CS mode, most of the residual stress was removed after artificial aging.
•The effect of clamping deformation on the material removal amount and cyclic material removal process on the residual stress are determined.•Energy equations under three-dimensional non-uniform ...residual stress field are established.•Excellent agreements of the machined surface shapes are obtained for predicted and experimental results.•The influence of cutting parameters and strategies on machining deformation is anlyzed.•The evolution of machining deformation in process is investigated.
Workpiece deformation under the coupling effect of clamping force, initial residual stress (IRS), and machining residual stress (MRS) is an essential concern in the manufacturing of thin-walled metallic parts. Prediction of machining deformations is critical for ensuring machining quality and has significant guiding implications for producing thin-walled parts. However, most research has been focused on calculating machining deformation caused by a single factor. Based on the energy principle, the effect of clamping deformation on the material removal amount and the effect of the cyclic material removal process on both IRS and MRS are analyzed. To predict the machining deformation of circular metallic plates, energy functions under the three-dimensional non-uniform residual stress field consider the coupling effect of multiple factors, which is established and solved by the Rayleigh-Ritz method. This analysis elucidates the formation mechanism of machining deformation under the single-factor effects of IRS and MRS as well as the coupling effect of clamping force and residual stress. In this article, an analytical prediction model with a prediction error of around 8.5% is established for machining deformation under the coupling effect. Additionally, leveraging the quantitative results of the proposed model, the impacts of cutting parameters and strategies on machining deformation, as well as the evolution of machining deformation throughout the entire material removal process are elicited.
•Welding residual stress predicted for WOL on PWR nozzle.•Effect of weld overlay sizing on residual stresses.•Reference for optimizing the weld overlay design.
Dissimilar metal welds are commonly ...used in various types of reactors to connect low alloy steel nozzles and austenitic stainless steel piping systems. To mitigate the degradation of stainless steel pipe welds that are affected by intergranular stress corrosion cracking in BWRs, weld overlays have been implemented to provide the structural reinforcement. They have also been applied to repair dissimilar metal welds at nozzles in BWRs and PWRs. A weld overlay can favorable reverse residual stresses from tensile to compressive around interior of the susceptible materials. The ASME Code Case N-504 series suggest that the evaluation of repaired welds should consider residual stresses that are generated by the weld overlay with other applied loads on the system. This study considers a dissimilar metal weld that joins the low alloy steel nozzle to the stainless steel safe end in a typical PWR, and is to calculate the post-overlay residual stress states using ANSYS finite element analysis software. Based on the stress report and site survey of the hot leg nozzle, models for analyzing residual stresses were developed on various assumptions. Computational results demonstrate that the weld overlay process probably provides compressive distributions of axial and hoop residual stresses at the inside surface of the dissimilar metal weld. The residual stress distributions that are induced by weld overlays of various sizes are compared to determine the effect of weld overlay sizing on the residual stresses in the original weld. The comparison reveals that weld overlay length has a greater effect on residual stresses than weld overlay thickness. As the applied overlay length increases, the compressive residual stresses increase markedly. Each nozzle/safe end design is somewhat unique; using a feasible weld overlay dimension in consideration of technical and economic is necessary. This investigation has provided a reference for optimizing the weld overlay design of dissimilar metal welds in PWRs.
•Four high strength steel (HSS) and eight hybrid I-sections were studied.•Welding effect on the material properties was investigated.•Residual stress measurements were conducted for HSS and hybrid ...I-sections.•A new residual stress distribution model is proposed.
High strength steel (HSS) I-sections are gaining increasing popularity compared with conventional strength steel counterparts, mainly due to its higher strength-to-weight ratio. Meanwhile, there has been growing interest in hybrid I-sections, which are made of different strength steels for flange and web plates, because of the increased need of maximising material utilization. This study investigates the welding effect on the material properties and residual stresses of welded HSS and hybrid I-sections. Tensile tests of coupons machined from both virgin plates and within the welded I-sections were carried out, followed by a metallographic analysis of welding position. It was found that the welding effect on the mechanical behaviour of steel materials varies, depending on the chemical composition and microstructure. Residual stress measurements for HSS and hybrid I-sections covering four web slenderness were conducted. The measurement results demonstrate that the effect of steel strength grade of constitutive plates on residual stress distribution of I-sections is negligible, and a new residual stress distribution model is proposed for welded HSS and hybrid I-sections examined in this study.
Surface treatments characterized by rapid heating and cooling (e.g. laser hardening) can induce very steep residual stress gradients in the direct vicinity of the area being treated. These gradients ...cannot be characterized with sufficient accuracy by means of the classical sin2Ψ approach applying angle‐dispersive X‐ray diffraction. This can be mainly attributed to limitations of the material removal method. In order to resolve residual stress gradients in these regions without affecting the residual stress equilibrium, another angle‐dispersive approach, i.e. the universal plot method, can be used. A novel combination of the two approaches (sin2Ψ and universal plot) is introduced in the present work. Prevailing limits with respect to profiles as a function of depth can be overcome and, thus, high‐resolution surface layer characterization is enabled. The data obtained are discussed comprehensively in comparison with results elaborated by energy‐dispersive X‐ray diffraction measurements.
This paper reports on high‐resolution analysis of residual stress gradients for a laser‐hardened surface layer using a combined angle‐dispersive X‐ray diffraction approach that applies the universal plot method and sin2Ψ evaluation.
In this study, the hot compression test of as-cast Mg-5Al-0.6Sc alloy was performed on Gleeble-3500 simulator, and the effect of deformation temperature (T: 250–400 °C) and strain rate (ε̇: 0.001 –1 ...s−1) on hot deformation mechanism of the alloy were systematically investigated. The thermal deformation behavior, microstructure evolution, texture and dynamic recrystallization (DRX) mechanism of the alloy were analyzed in detail by combining the constitutive equation, processing map and electron backscatter diffraction (EBSD) technology. The results demonstrated that the flow stress decreased with the increase of T and decrease of ε̇. The established constitutive equation could accurately predict the hot deformation behavior of the alloy, and the calculated average activation energy (Q) is 144.58 kJ/mol. Based on processing map, the optimal processing area is within 300–350 °C, 0.001 s − 1 and 350–400 °C, 0.001 s−1 - 0.01 s−1. The microstructure at 350 °C and 0.001 s−1 is more uniform and exhibits low residual stress level. The increase of T and decrease of ε̇ are both conducive to the occurrence of DRX. DRX mechanism includes discontinuous DRX (DDRX), continuous DRX (CDRX), deformation twin induced DDRX and CDRX. In addition, both DRXed grains and unDRXed grains showed typical // CD texture. Combined with the in-grain misorientation axis (IGMA) analysis, when T is 250 °C and 300 °C, the deformation is dominated by basal dislocations and prismatic dislocations, and the proportion of twinning and DRX is extremely low. When T is 350 °C and 400 °C, the pyramidal Ⅱ<c+a>dislocations is activated greatly, and the DRX fraction increases significantly, which become the predominant deformation mechanism.
•The hot deformation behavior of a new Mg-5Al-0.6Sc alloy was investigated.•The effects of the temperatures and strain rates on microstructure evolution and deformation mode were analyzed.•Different DRX mechanisms and their effects on texture are discussed in detail.
In light of the demand for reducing the emission of climate-damaging gases such as CO2, it is very important to apply lightweight materials in the aerospace and automotive industries. In the past ...years, hybrid structures made of carbon fiber reinforced plastics (CFRP) and metals received high attention from numerous industries. Laser welding is an advanced approach for bonding dissimilar materials. However, in the welding process, residual stresses are induced in the joined part, which influence the mechanical performance of the bonded components. In the present work, residual stresses in laser welded CFRP and steel joints are experimentally determined using the hole drilling method (HDM) and numerically analyzed by thermal elastic–plastic finite element analysis. The non-uniform residual stress distribution through the thickness direction of the CRRP and steel plates can be successfully measured when the anisotropic material properties in CFRP are considered. Moreover, a numerical simulation was carried out for analyzing the residual stresses in the laser welded CFRP/steel joints, particularly their distribution characteristics at the CFRP/Steel interface. Specific discussions focus on the residual stress formation mechanism and the effect of laser welding process parameters on the residual stresses through experimental tools and numerical simulations.
Abrasive waterjet peening (AWJP) has been used to modify the mechanical properties of components by introducing plastic deformation and compressive residual stress (CRS) into the workpiece surface. ...The present study aims to investigate the influence of different AWJP parameters on the surface integrity of Inconel 718 alloy. The AWJP with different pump pressures, standoff distances, traverse speeds, and abrasive flowrates are conducted on the Inconel 718 workpiece. The surface integrity response including surface topography, CRS, hardness, and microstructure of AWJP are investigated, and different AWJP parameters effect on changing trend of surface integrity response is discussed. Results show that the AWJP-treated workpiece with different parameters formed a footprint width of 3.0–4.3 mm, the key factor effect on footprint width is standoff distance. The maximum surface roughness of Sa = 9.06 μm occurs at pump pressure 300 MPa, and pump pressure is more sensitive than other AWJP parameters' effect on surface fluctuation and surface roughness. The thickness of the stress layer is approximately 100–180 μm, and the maximum CRS is larger than 1100 MPa. Pump pressure and standoff distance are two main factors that effect on CRS, while the changing rate effect on CRS is gradually slow with the increase of pump pressure and the reduction of standoff distance. The maximum hardness increases more than 20 % from 490 to 590 HV at a pump pressure of 300 MPa. The pump pressure is the key factor influencing on micro-hardness. The microstructure evolution on the sub-surface of AWJP treated workpiece was characterized by SEM and EBSD, which showed that grains refine and strengthening layer formed on the top surface of the AWJP-treated workpiece surface, also the cracks at pump pressure 300 MPa. The results revealed that AWJP has great development potential in Inconel 718 surface treatment, and pump pressure is the key factor that effect on surface integrity.
•Abrasive waterjet peening (AWJP) was performed on Inconel 718 alloy.•Surface topography surface roughness Sa is mainly affected by pump pressure.•The compressive residual stress (CRS) induced by AWJP is larger than 1000 MPa.•Maximum hardness occurs at pump pressure 300 MPa and increases larger than 20 %.•The near-surface grains are significantly refined with the action of the AWJP.
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