Search Results (28)

Quench–polish–quench (QPQ) nitro-carburizing of AISI 4140 steel in a salt bath was performed in this study. Nitro-carburizing in a salt bath enhanced the formation of Fe-nitride on the outer surface layer. Moreover, the oxidizing treatment formed a thin oxide layer decorated on the outermost part of the QPQ-treated sample. The dense compound layer formed after nitro-carburizing in a salt bath consisted of refined granular Fe₃N and transformed to Fe₂N after post-oxidation treatment. Micro-shot peening (MSP) was adopted before QPQ treatment to increase the treated steel’s fatigue performance. The results indicated that MSP slightly increased the thickness of the compound layer and harden depth, but it had little effect on improving the fatigue strength/life of the QPQ-treated sample (SP-QPQ) compared to the non-peened one (NP-QPQ). A deep compressive residual stress (CRS) field (about 200 μm) and a hard nitrided layer showed a noticeable improvement in the fatigue performance of the QPQ-treated ones relative to the 4140 substrates tempered at 570 °C. The ease of slipping or deforming on the substrate surface was responsible for its poor resistance to fatigue failure. The cracking and spalling of the brittle surface layer were the causes for the fatigue crack initiation and growth of all of the QPQ-treated samples fatigue-loaded at/above 875 MPa. It was noticed that fatigue crack initiation at the subsurface inclusions was more likely to occur in the SP-QPQ sample fatigue-loading at 850 MPa or slightly above the fatigue limit. Full article

Heat-performance nickel-based superalloys are commonly applied in various critical industries. In this work, test samples in the form of turbine blades were manufactured by means of laser powder bed fusion (LPBF) 3D technology. This research focused on comparison of the influences of various surface finishing methods. The mechanical surface post-processing of the LPBF-manufactured Inconel 718 alloy samples consisted of ultrasonic impact treatment (UIT), ultrasonic shot peening (USP), shot peening (SP), and barrel finishing (BF). The surface microrelief was evaluated using a high-precision laser profilometer, while the microstructural features were studied by light optical microscopy (LOM), scanning/transmission electron microscopy (SEM/TEM), and X-ray diffraction (XRD). Potentiodynamic polarization tests were also conducted to compare the surface finishing methods in terms of corrosion resistance improvement of the LPBF-manufactured 718 alloy samples. The effects of the surface microstructure and hardening intensity in combination with residual stresses and surface relief coupled with roughness profile shapes on the room temperature corrosion behavior of plastically deformed 718 alloy specimens manufactured by LPBF were studied. The corrosion rate (CR) of the LPBF-manufactured samples was reduced after post-processing: BF (~16 μm/year), USP (~15 μm/year), SP (~6.5 μm/year), and UIT (~5.5 μm/year). The experimental trends also agreed well with the theoretical trends of uniform corrosion of the studied alloy. Full article

The number of easily destroyed parts with high value is increasing in industry, and green remanufacture engineering is now mainstream in this new and expanding industrial field. Equal–additive–subtractive manufacturing, as a new technology that combines strengthening technology, additive manufacturing, and machining technology has great potential for development in the area of remanufacturing. Aiming at the damage characteristics of a plunger rod, this paper carries out a study about the repair technology by equal–additive–subtractive manufacturing of laser-directed energy deposition and shot peening. It was found that the microstructure of the materials repaired by equal–additive–subtractive technology is finer and the tensile strength can reach 100.4% of the base material. The surface residual stress of cladding materials changes from tensile stress to compressive stress, which reduces forming defects. Equal–additive–subtractive manufacturing has great significance in expanding the application of hybrid manufacturing and promoting green remanufacturing of parts with high value. Full article

Total hip arthroplasty (THA) is a surgical procedure for patients with pain and difficulty walking due to hip osteoarthritis. In primary THA, the acetabulum and femoral head are replaced by a prosthesis where the modular femoral head and inner liner of the acetabulum form the bearing surface. The most popular bearing surface used in the United States, metal-on-polyethylene, consists of a cobalt–chromium molybdenum (CoCrMo) alloy femoral head that articulates with a polyethylene acetabular liner, typically made of highly cross-linked polyethylene. While successful in most cases, THA sometimes fails, commonly from aseptic loosening due to the wear debris of polyethylene. Fine-particle shot peening (FPSP) is a simple method for enhancing the mechanical properties and surface properties of metal, including reducing friction and enhancing the lubrication properties of the metal surface. In this study, we applied FPSP to the CoCr in the femoral head of a hip prosthesis to improve its surface properties and conducted experiments with pin-on-disc tribometers using CoCr as a pin and highly cross-linked polyethylene as a disc to mimic the THA implant. The results show that FPSP significantly enhances the tribological properties of the CoCr surface, including lubrication; decreases the friction coefficient; and decreases the polyethylene wear volume. Full article

Austenitic stainless steels used in structural applications suffer from stress corrosion cracking due to residual stresses during welding. Much research is being conducted to prevent the stress corrosion cracking of austenitic steels by inducing compressive residual stresses. One method is ultrasonic shot peening (USP), which is used to apply compressive stress by modifying the mechanical properties of the material’s surface. In this study, 304L stainless steel was butt-welded by gas tungsten arc welding (GTAW) and subsequently subjected to compressive residual stress to a depth of 1 mm from the surface by a USP treatment. The influence of USP on microstructural changes in the base metal, the HAZ and weldment, and the corrosion properties was analyzed. A microstructural analysis was conducted using SEM-EDS, XRD, and EBSD methods alongside residual stress measurements. The surface and cross-sectional corrosion behavior was evaluated and analyzed using a potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS) measurements, a double-loop electrochemical potentiokinetic reactivation (DL-EPR) test, and an ASTM A262 Pr. C test. The surface was deformed and roughened by the USP. The deformed areas formed crevices, and the inside of the crevices contained some cracks. The crevices and internal cracks caused pitting, which reduced the resistance of the passivation film. The cross-section was subjected to compressive residual stress to a depth of 1 mm from the surface, and the outermost area of the cross-section had fine grain refinement, forming a solid passivation film that improved the corrosion resistance. Full article

This literature review indicates that the basic microstructure of Ti6Al4V is bimodal, consisting of two phases, namely α + β, and it occurs after fabrication using conventional methods such as casting, plastic forming or machining processes. The fabrication of components via an additive manufacturing process significantly changes the microstructure and properties of Ti6Al4V. Due to the rapid heat exchange during heat treatment, the bimodal microstructure transforms into a lamellar microstructure, which consists of two phases: α′ + β. Despite the application of optimum printing parameters, 3D printed products exhibit typical surface defects and discontinuities, and in turn, surface finishing using shot peening is recommended. A literature review signalizes that shot peening and electropolishing processes positively impact the corrosion behavior, the mechanical properties and the condition of the surface layer of conventionally manufactured titanium alloy. On the other hand, there is a lack of studies combining shot peening and electropolishing in one hybrid process for additively manufactured titanium alloys, which could synthesize the benefits of both processes. Therefore, this review paper clarifies the effects of shot peening and electropolishing treatment on the properties of both additively and conventionally manufactured Ti6Al4V alloys and shows the effect process on the microstructure and properties of Ti6Al4V titanium alloy. Full article

High-entropy alloys (HEAs) are prospective advanced materials for the production of components that operate at high, severe friction and in high-temperature environments. This is because they possess unique properties requisite for such applications. Hence, this study was aimed at reviewing most recent publications on the tribological characteristics of HEAs processed with spark plasma sintering (SPS). The choice of SPS was because it impacts alloys with a homogenous microstructure, high wear resistance, densely packed grains, and nanocrystalline microstructure. The resource materials for this study were obtained from the Scopus-indexed journal/Google Scholar website for articles published within the last five years. From the study, it was observed that HEAs have good tribological properties which permit their prospective usage in the production of strength-demanding, wear-demanding, and temperature-demanding components. The addition of BCC-forming and FCC-forming elements would help in improving the wear properties of HEAs. It was also observed from the literature that the incorporation of post-processing treatment, laser cladding, shot peening, or the coating of SPSed composites would increase the effective performance and durability of HEAs prepared with SPS. Full article

Two austenitic stainless steel (ASS) plates, 304L and 316L, were cold-rolled (304R and 316R) with a 10% reduction in thickness and then subjected to laser welding. Cold rolling caused slight surface hardening and introduced residual tensile stress into the ASS plates. The susceptibility to stress corrosion cracking (SCC) of the welds (304RW and 316RW) was determined using the U-bend test pieces in a salt spray. To highlight the stress concentration at the weld’s fusion boundary (FB), the top weld reinforcement was not ground off before bending. Moreover, micro-shot peening (MSP) was performed to mitigate the SCC of the welds by imposing high residual compressive stress and forming a fine-grained structure. Cold rolling increased the susceptibility of the 304R specimen to pitting corrosion and intergranular (IG) microcracking. Moreover, pitting corrosion and SCC were found more often at the FBs of the 304RW. The corrosion pits of the peened 304RW (304RWSP) were finer but greater in amount than the those of the un-peened one. The results also indicated that the 316L ASS welds with MSP were resistant to the incidence of pitting corrosion and SCC in a salt spray. The better reliability and longer service life of dry storage canisters could be achieved by using 316L ASS for the construction and application of MSP on it. Full article

An equiatomic CrCoNi medium-entropy alloy was subjected to high-energy shot peening (HESP) to fabricate a gradient nanostructure (GNS) in this work. The microstructures of the GNS samples at different depths within the deformed layer were thoroughly investigated. The microstructure exhibited a transformation from unstressed coarse grains to deformed coarse grains, followed by the formation of ultrafine grains, and ultimately reaching a final nanocrystalline structure with a uniform size of approximately 50 nm. Detailed structural analysis indicated that the deformation process was primarily influenced by the interaction between dislocations and deformation twins, which was attributed to the low stacking fault energy (SFE) of the alloy. The nanocrystalline mechanism was divided into three stages. In the coarse-grained deformation stage, the dislocation band divided twin/matrix lamellae into sub-segments, and the cross twin divided coarse grains into ultrafine grains simultaneously. In the ultrafine grain deformation stage, dislocations were arranged around the deformation twins in order to break the twins to form incoherent boundaries, destroying the coherent relationship between the twin and matrix. Finally, in the nanocrystalline deformation stage, the nanocrystalline structure was further divided into smaller segments to accommodate additional strains through the interaction between dislocations and twins. Full article

The FeCoNiCrMo_0.2 high entropy alloy coatings were deposited on BS960 high strength steel by plasma spraying method with four different current intensities (250 A, 350 A, 450 A, 550 A). These coatings were then subjected to a subsequent micro-shot peening treatment. Surface characteristics including surface morphology, microhardness and phase composition were characterized, and the wear resistance of the coatings was assessed by reciprocal friction and wear tests. The results showed that the high entropy alloy coatings had FCC structure. XRD results showed that no new phase was formed during the spraying process. At the same time, shot peening treatment could effectively improve the hardness of the coating surface. Under the four processes, the coating surface prepared with the current intensity of 350 A had the highest microhardness and uniformity before and after shot peening, and the hardness values were 473 ± 10.21 and 504 ± 8.62 HV_0.2, respectively. The friction and wear test results showed that the friction coefficients of the four coatings were close to each other at 10 N load, which was about 0.4. When the test load reached 25 N, the friction coefficient of the coating with current intensity of 350 A was lower, and it showed better friction performance. After shot peening, the friction coefficient of the four coatings further decreased to about 0.3 under 10 N loading due to the existence of hardened surface layer. When the test load reached 25 N, the hardened layer would be worn through and the friction coefficient would suddenly rise. Under the 25 N test load, the hardened layer of the high-entropy alloy coating with current intensity of 350 A illustrated better friction resistance. Full article

Micro-shot peening on AISI 304 and 316 stainless steel (SS) laser welds was performed to evaluate its effect on the susceptibility to stress corrosion cracking (SCC) in a salt spray containing 10% NaCl at 80 °C. The cracking susceptibility of the welds was disclosed by testing U-bend specimens in a salt spray. Micro-shot peening caused an intense but narrow deformed layer with a nanocrystal structure and residual compressive stress. Austenite to martensite transformation occurred heavily on the top surface of the micro-shot peened welds. SCC microcracks were more likely to be initiated at the fusion boundary (FB) of the non-peened welds. However, fine pits were formed more easily on the micro-shot peened 304 fusion zone (FZ), which was attributed to the extensive formation of strain-induced martensite. The nanograined structure and induced residual compressive stress in the micro-shot peened layer suppressed microcrack initiation in the 304 and 316 welds in a salt spray. Compared with the other zones in the welds in a salt spray, the high local strain at the FB was the cause of the high cracking susceptibility and could be mitigated by the micro-shot peening treatment. Full article

The effect of shot peen forming on the corrosion-resistant of 2024 aluminum alloy in a salt spray environment was studied with an electrochemical workstation. The surface morphology and cross sectional morphology of the original and shot peen-formed sample were studied by a scanning electron microscope. After shot peen forming, the salt spray corrosion resistance of 2024 aluminum alloy was worsened (the corrosion rates of the original alloy and the shot peen-formed alloy were 0.10467 mg/(cm²·h) and 0.27333 mg/(cm²·h), respectively, when the salt spray corrosion time was 5 h). The radius of capacitive reactance arc of the sample subjected to shot peen forming was smaller than that of the original sample. When the salt spray corrosion time was 5 h, the doping density (N_A) of the original alloy was 2.5128 × 10⁻¹³/cm³. After shot peen forming, the N_A of the alloy increased to 15 × 10⁻¹³/cm³. For the shot peen-formed sample, pitting corrosion first occurred in the crater lap zone and became severe with salt spray time. The cross sectional morphology of both original and the shot peen-formed samples shows that severe intergranular corrosion occurred in the salt spray environment. However, for the original sample, the intergranular corrosion distribution was lamellar. For shot peen-formed sample, the intergranular corrosion distribution was network. Full article

In this study, a novel approach for residual stress (RS) distribution on forged AA7175 is considered to replace and simplify the manufacturing process, based on the lean manufacturing concept. AA7175 alloy is a quench-sensitive material applied in the aeronautics industry, which is subjected to vibration and cyclic loads leading to fatigue failure. Generally, costly postprocessing operations, such as shot peening, are used to modify RS on the surfaces of parts. Considering the fact that this operation is usually performed manually and is costly, the industrial sectors have been searching for an alternative to simplify the process. Here, quenching and T74 aging are found to advantageously modify RS distribution by forming compressive RS on parts’ surface layers. The proposed heat treatment allows for the removal of the shot-peening process, helping to reduce the costs associated with the manufacturing process and to increase production quality. Full article

The effects of shot-peen forming on the fatigue properties of aluminum alloy samples were measured with a mechanical testing & simulation (MTS) tester in atmospheric and salt-spray environments. After shot-peen forming, the fatigue performance of the aluminum alloy sheet was significantly improved in both the atmospheric and the salt spray environment. Compared with the detail fatigue rating (DFR) value in the atmospheric environment, in the salt-spray environment, the DFR value of the original samples decreased to 110.82 MPa, decreasing by 4.47%. The DFR value of the shot-peen-forming samples decreased to 151.03 MPa, decreasing by 11.40%. Fatigue fracture characteristics demonstrate that the number of crack sources decreased after shot peening. However, the corrosion rate test in a neutral saline environment showed that the corrosion resistance of the aluminum alloy sheet decreased after shot peening. In the salt-spray environment, surface residual-stress analysis showed that there was about 30 MPa tensile stress on the original sample, and 100 MPa compressive stress on the shot-peened sample. Therefore, the improvement in the fatigue resistance of the aluminum alloy sheet after shot peening was largely due to the residual compressive stress introduced on the surface of the aluminum alloy. Full article

In this paper, the corrosion resistance of four GCr15 steel samples has been investigated. Three samples were initially surface-treated by ultrasonic shot peening (USP), a dry ultrasonic strengthening grinding process (DUSGP), and a wet ultrasonic strengthening grinding process (WUSGP), respectively, while another one was only polished. Then, all the processed samples were subjected to salt spray corrosion. Sample properties, such as capacitance arc, self-corrosion potential (E_corr), self-corrosion current density (I_corr), corrosion morphology, and corrosion products were analyzed. Results show that the sample treated by WUSGP has the best corrosion resistance, which can be attributed to the high dislocation density, small grain size, needle-like and lath-like shape of martensite content formed in the treatment, which hinders Cl⁻ from eroding the matrix. The obtained corrosion pits and cracks in Sample WUSGP show a width of approximately 1.4 µm and 2.1 µm, respectively, degrading 78% and 75% compared to polishing. The possible corrosion mechanism of the samples has been discussed. The findings denote that the treatment fused ceramic balls, strengthened liquid, and corundum in USP could be an efficient method to improve the corrosion resistance of some mechanical parts. Full article