The internal stress states of Optimized ZIRLO (OPZ) samples are evaluated post-quenching from increasing temperatures to determine the role of chromium coatings, oxidation, and microstructural ...reorienting on internal stress state. Before substantial oxide development (under 700 °C), uncoated tubular samples freely expand and do not accumulate significant global internal stress. As a stable, passivizing oxide develops (700–900 °C), a complex stress state develops with both the interior and exterior oxides in hoop compression. The internal tensile stress increases until the sample fully oxides, and biaxial stress is released through tortoiseshell-like cracking mechanisms. When a chromium coating is introduced, the initial stress states at low temperatures are higher than the uncoated samples due to Cr-coating application techniques and material differences between Cr and OPZ. At higher temperatures (700–1100 °C), the Cr-coated samples undergo a much simpler stress state than the uncoated samples due to the tensile hoop stress state of the Cr-coating caused by differing thermal expansion and the compressive state of the internal oxide caused by a Pilling-Bedworth ratio > 1. The subsequent film cracking mechanisms also differ from the uncoated samples. The smoother stress state experienced by the Cr-coated vs uncoated OPZ samples allows the Cr-coated samples to maintain the circular geometry that is vital to their protective application in nuclear reactors.
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•The mechanism of residual stress relaxation in carburized steel was elucidated.•The compressive residual stress relaxation was attributed to compressive yielding.•The fatigue limit ...was estimated considering residual stress relaxation.•The compressive residual stress contributing to increased fatigue limit was revealed.
The mechanism of residual stress relaxation for carburized steels was elucidated and their fatigue limit was estimated. The compressive residual stress in the carburized steel after rotating bending fatigue tests is mainly influenced by the relaxation during the compressive loading phase, although it increases at the early stage. The fatigue limit of carburized steels can be estimated according to the modified Goodman diagram considering the residual stress relaxation. The proposed equation shows the maximum value of the fatigue limit (1013 MPa) of carburized steel and the maximum value of the compressive residual stress contributing to the increased fatigue limit.
The distortion in machining aeronautical aluminum alloy parts (AAAPs) is one of the serious challenges in the aviation industry, and the residual stresses produced in multimanufacturing steps are the ...main cause. In order to get a comprehensive understanding of the problems about residual stresses and distortion in machining AAAPs, the state-of-the-art in several aspects including the generation reasons of residual stresses, the factors influencing distortion during machining, the measurement methods of residual stresses, the prediction and controlling methods of distortion are summarized in this paper. The generation mechanism of the bulk residual stress inner materials and the machining-induced residual stresses, as well as the factors affecting two kinds of residual stresses are stated. Also, the influences of residual stresses and machining process conditions on distortion are analyzed. Furthermore, the common residual stress measurement methods and its application scope are summarized. Significantly, the differences, advantages, and disadvantages of various prediction methods are analyzed. The methods of controlling distortion before and after machining are summarized. Finally, the paper gives out further research on the distortion in machining AAAPs in aeronautical manufacturing.
This paper presents a recent study on weld residual stress relief mechanisms associated with furnace-based uniform post-weld heat treatment (PWHT). Both finite element and analytical methods are used ...to quantitatively examine how plastic deformation and creep relaxation contribute to residual stress relief process at different stages of PWHT process. The key contribution of this work to an improved understanding of furnace based uniform PWHT can be summarized as follows:(1)Plastic deformation induced stress relief during PWHT can be analytically expressed by the change in material elastic deformation capacity (or elastic deformation limit) measured in terms of material yield strength to Young's modulus ratio, which has a rather limited role in overall residual stress relief during furnace based uniform PWHT.(2)The most dominant stress relief mechanism is creep strain induced stress relaxation, as expected. However, a rapid creep strain development accompanied by a rapid residual stress reduction during heating stage before reaching PWHT temperature is shown to contribute to most of the stress relief seen in overall PWHT process, suggesting PWHT hold time can be significantly reduced as far as residual stress relief is concerned.(3)A simple engineering scheme for estimating residual stress reduction is proposed based on this study by relating material type, PWHT temperature, and component wall thickness.
•The paper clarified effects of plastic deformation and creep relaxation on weld residual stress relief during uniform PWHT.•Creep strain development is far more important than plastic strain, mostly completed even before hold time starts.•Plastic strain development is insignificant and be analytically described by a material elastic deformation capacity parameter.•An engineering estimation scheme is proposed for determining residual stress reduction resulted from furnace based PWHT.
The deposition of ternary nitrides with the incorporation of carbon atoms into its structure has demonstrated to be a promising approach in the pursuit of wear-resistant and self-lubricating ...coatings. Firstly, both TiAlN and TiAlCN monolayers were deposited using direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) onto quenched and tempered AISI H11 tool steel to be used as references. Acetylene was used as a carbon precursor, producing DCMS and HiPIMS TiAlCN coatings with 9.0 and 21.7 at.% C, respectively.
Subsequently, TiAlN/TiAlCN multilayers of various designs were also developed as follows: 5×10/500, 5×50/500 and 5×100/500 nm. Residual stresses of the coating systems were determined by X-ray radiation utilising an ETA-diffractometer with a Cu-Kα radiation source applying the sin2ψ method. Additionally, residual stresses depth gradients of the substrate before and after the deposition of the coatings were determined in a LEDDI 8-circle diffractometer equipped with a W-X-ray tube and operated in the energy-dispersive mode of diffraction. Great reduction of the compressive residual stresses in the coatings was observed after the introduction of carbon into the TiAlN coating structure, shifting from −1047 ± 149 to −307 ± 211 MPa for the DCMS and from −7035 ± 1361 to +989 ± 187 MPa for the HiPIMS coatings. In the multilayer coatings, compressive residual stresses increase along with the increment of the TiAlN interlayer. Additionally, residual stresses of the substrate in the near-surface are dragged from low compressive stresses (−218 ± 61) to tensile stresses in the range of 1000 to 2000 MPa for all the DCMS/substrate systems, a behaviour only presented in HiPIMS by the TiAlN monolayer. Wear coefficients of all the evaluated HiPIMS systems are notoriously lower than their DCMS counterparts. Compared to TiAlN, TiAlCN HiPIMS presented a lower coefficient of friction but a higher wear coefficient, which in turn was not reduced by the introduction of the multilayer systems. Finally, Scratch test and Rockwell C adhesion tests have shown higher adhesion of DCMS coatings than HiPIMS coatings, and a detriment of the monolayers adhesion by the implementation of TiAlN/TiAlCN multilayer systems. The understanding of the residual stresses, both in the coating and in the substrate, and the way they affect the tribomechanical performance of the system coating/substrate continues to be of great importance, especially for coatings deposited by new technologies such as HiPIMS and self-lubricating coatings.
•Great reduction of compressive residual stresses with the carbon inclusion in TiAlN.•High superficial residual stresses on the substrate after DCMS deposition.•Adhesion of DCMS coatings systems to AISI H11 is always higher than HiPIMS.•Ceramic/ceramic multilayer designs did not improved adhesion or wear.
In most literature, the residual stress distribution is assumed to be a symmetrically 2nd order polynomial with compressive stresses near the surface, balanced by tensile stresses in the centre. This ...assumption leads directly to the assertion that the thickness of the compressive layer is 21.1% of the total thickness. The present paper experimentally investigates the accuracy of this well-established rule for thermally tempered glass and develops a simple equation for asymmetric stress distributions.
The experimental investigation is based on more than 6000 measurements of commercially tempered (and heat-strengthened) soda lime silica glass and provides statistics for the compressive zone depth. The dependency of the thickness, residual stress state, and the effect of asymmetric stress distributions is investigated.
Due to the scattering in the experimental results, an FE-model has been applied to clarify the effect from the different parameters.
•A large experimental campaign is investigating the compressive zone depth in tempered glass.•Commonly used assumptions are investigated and deviations are reported.•FE models are used for investigating the theoretical influence of different parameters on the compressive zone depth.
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This work aims at quantitative analysing the effect of different microstructures on the velocity at stress-free and stress coefficient (K) of longitudinal critical refraction (LCR) ...wave in measuring welding residual stress process, ameliorating the traditional LCR wave method for improving its’ effectiveness and accuracy. The longitudinal critically refracted wave attenuation velocity (LCR-AV) method was proposed in the evaluation of residual stresses in A7N01 welded joints. The same initial status base materials samples are used to produce different levels of grain size and precipitation by heat treatment technology, obtained the velocity at stress-free and attenuation of LCR wave. As expected, the voltage amplitude changes linearly with velocity and stress coefficient, and the precipitation effect can be ignored. The LCR-AV method based on the liner relationship between velocity, attenuation and grain size are efficient to decrease the errors resulting from the different microstructure (base metals, heat-affected zones, and welded zones). Differ with the traditional LCR waves method, the LCR-AV method also measures the voltage amplitude, and the measured results of LCR-AV method compared with those obtained by the hole-drilling reference method shows more sufficient measurement reliability and precision. It shows that LCR-AV method is a valuable quantitative technology to estimate the residual stress of welded joints.
Metal additive manufacturing (MAM) technology has great application potential in the aerospace, medical and energy fields with its high material utilization efficiency to achieve the manufacturing of ...metal parts of any shape. However, the extreme thermal, mechanical, and metallurgical coupling in MAM process leads to large residual stresses in the manufactured samples. Residual stress has a significant effect on the dimensional stability, corrosion resistance, crack growth resistance and mechanical properties of MAM samples. As a result, residual stress can be regarded as a key factor in controlling costs, enhancing product efficiency and quality. To help researchers and engineers attain up-to-date information and knowledge about residual stress in MAM, the current paper provides a comprehensive review in this field, especially the formation mechanisms, the influence of process parameters, prediction and control methods.
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