Surface Microstructure Evolution Research Articles

Research on the surface modification and microstructure evolution during gear profile grinding based on cellular automaton

The matrix structure of high-strength gears mainly comprises martensite with high stacking fault energy. The dominant mechanism of microstructure evolution in the surface layer during profile grinding is continuous dynamic recrystallization. However, the understanding of continuous dynamic recrystallization structure evolution during gear profile grinding remains limited. In this study, a predictive model based on cellular automaton for martensite structure evolution during gear profile grinding is proposed. Coupled with the finite element method, the microstructure evolution prediction of high-strength steel gears in profile grinding is conducted. The proposed model demonstrates good consistency with experimental data in calculating the proportion of low angle grain boundaries during grinding process. By combining experimental and theoretical prediction results, the mechanism of the influence of grinding depth on grain refinement in surface layer during gear profile grinding is elucidated. The dislocation density increases with the increase of grinding depth, leading to the generation and transformation of more subgrains. By analyzing the grain size and the proportion of subgrain boundaries, an optimal grinding depth threshold under dry grinding conditions is determined. This study provides valuable insights into the continuous dynamic recrystallization structure evolution during gear profile grinding process.

Influence of laser treatment on the microstructural evolution and performance of Ti65 alloy

Achieving simultaneous increase in strength and plasticity of metallic materials is a long-term challenge. In this study, we prepared the Ti65 alloy with surface refined structure by laser treatment and studied the evolution of surface and cross-sectional microstructure, as well as its impact on tensile properties. The tensile strength of the Ti65 alloy sheet increases from 1098 to 1136 MPa after laser treatment, and the average fracture strain significantly rises from 6.81% to 10.23%, marking a substantial 50.2% increment. During laser treatment, the fast cooling rate caused the formation of a strengthening layer with fine grains, which leads to an increase in strain hardening rate and non-uniform deformation induced strengthening provided by non-uniform structures. The findings in this work provide a new routine for upgrading mechanical properties of titanium alloy through generating a strengthening layer with fine grains on the surface.

The influence mechanisms of re-fused scanning on the surface roughness, microstructural evolution and mechanical properties of laser powder bed fusion processed AlMgScZr alloy

Laser powder bed fusion (LPBF) stands out as the foremost method for achieving intricate structure with superior design flexibility among additive manufacturing technologies. Within the LPBF process, surface roughness serves as a critical metric governing both fabrication precision and build quality. This study delves into the evolution of the top and side surface roughness as re-fused scanning times increase in LPBF-fabricated AlMgScZr alloy. Concurrently, the investigation evaluates alterations in microstructural characteristics and mechanical properties. Various characterization techniques, including confocal laser scanning microscope, scanning electron microscope, X-ray diffraction, electron backscatter diffraction, as well as tensile and microhardness tests, are employed. The findings concerning the top surface reveal that the initial application of re-fused scanning contributes to enhanced surface roughness. This improvement stems from refined grain structures and induced lattice distortions, facilitated by rapid heat dissipation and thermal recycling within the solidified layer. Consequently, microhardness increases. However, introducing the subsequent re-fused scanning exacerbates surface roughness and instigates Marongoni flow instability, magnesium depletion, and alterations in lattice structures. Moreover, with increasing the re-fused times, there is a noticeable enhancement in preferential crystallite growth orientation along the (200)α-Al crystal plane. Regarding the side surface, escalating re-fused times correlate with deteriorating roughness and alterations in molten pool shape and size, attributable to successive energy input. Despite these surface variations, minimal differences are observed in yield strength, tensile strength, and elongation. In essence, this research offers valuable insights into selecting optimal scanning methodologies during the LPBF process, thus guiding improvements in fabrication precision and component quality.

Surface Damage and Microstructure Evolution of Copper-Containing Antibacterial Stainless Steel During Quasi-In Situ Tensile Process

Surface Damage and Microstructure Evolution of Copper-Containing Antibacterial Stainless Steel During Quasi-In Situ Tensile Process

Correlation between the micro-shot peening coverage and surface microstructural evolution and fluoride-induced corrosion behavior in Monel 400 alloy

This study examines the influence of micro-shot peening (MSP) on Monel 400 alloy, focusing on surface microstructural evolution and fluoride-induced corrosion behavior compared to its solution annealed (SAed) counterpart. MSP treatments were conducted at various surface coverages (100%, 200%, 500%, 1000%, 1500%, and 2000%). Characterization encompassed microhardness, surface roughness, grazing incidence x-ray diffraction (GI-XRD), field emission scanning electron microscopy (FE-SEM) with electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). With increasing the MSP coverage to 2000%, the surface crystallite size decreased from approximately ∼30 µm in the SAed sample to 60 nm. TEM analysis emphasized dislocation slip and formation of dislocation structures as the primary mechanisms for the grain refinement. However, the 2000% coverage exhibited microcrack formation, compromising its hydrofluoric (HF) corrosion resistance. Electrochemical tests revealed severe localized corrosion in all MSP-treated samples except the 1500% coverage, which exhibited a minimum passive current density of 0.2–1.0 µA/cm2. Inductively coupled plasma optical emission spectroscopy (ICP-OES) of immersion solutions showed lower copper and nickel ion concentrations (<150 ppm) in the 1500% MSP-treated sample, indicating its enhanced corrosion resistance. X-ray photoelectron spectroscopy (XPS) identified NiO, NiF2, CuO, CuF2, and Cu(OH)2 phases in SAed and 1500% MSPed samples, with a higher concentration of copper oxide (CuO) in the corrosion film of the 1500% MSP-treated sample, contributing to its superior corrosion resistance.

Surface topography and microstructure changes of ultrafine-grained graphite prepared from filler of onion-like carbon spheres by Xe ions irradiation

Onion-like carbon spheres (OLC) were doped into the traditional graphite raw material system to decrease the pore diameter to ∼400 nm, with potential for use in molten salt reactors. The obtained graphite (OLCG) prepared from OLC was subjected to 7 MeV Xe26+ irradiation in this work, and a systematic investigation was conducted to verify its irradiation behavior. The surface morphology and microstructural evolution in graphite samples under different irradiation conditions were studied with different characterization methods. The surface roughness of OLCG increased and the hill appeared at lower irradiation doses, which was similar to that of IG-110, but the filler particles of OLCG gradually become spherical at 2.5 dpa. The analysis by X-ray diffraction reveals that OLCG's graphitization degree is approaching but slightly worse compared to IG-110. Raman studies indicate that the irradiation causes an increase in defect density and in-plane disorder both in graphite. The OLC filler exhibits a greater sensitivity to radiation, leading to OLCG being slightly sensitive to radiation as compared to IG-110. Neutron irradiation of the resulting graphite should be continued as OLCG showed good irradiation resistance at low irradiation doses and had a much smaller pore diameter.

Evolution of surface microstructure of Re‐Al‐Ni‐Au based ohmic contacts on n‐type GaN

AbstractRecently, rhenium (Re) based ohmic contacts to GaN have been studied for their low resistivity, smooth surface morphology, and sharp edge acuity at low annealing temperatures. In this work, we discuss the evolution of surface microstructures for Re‐Al‐Ni‐Au ohmic contacts on n‐GaN as a function of Re layer thickness and annealing temperature. For all Re thicknesses, the Al and Ni segregate into agglomerates that increase in size with increasing annealing temperature. These agglomerates are surrounded by Al‐Au films. Along with the underlying Re layer, they form different crystallographic phases of Re‐Al‐Ni, Al6Re, AlAu2, and Al2Au5. This, along with the formation of Re‐N phases at the metal‐semiconductor interface leads to low resistivity ohmic contacts on n‐GaN. Investigating the evolution of the contact microstructure is an important step in understanding the behavior of the Re‐based ohmic contact system.

Investigation on the damage mechanism of micro-cutting surface layer of aluminum alloy 7075 with different heat treatment processes

This paper investigates the machinability and microscopic surface damage mechanisms of aluminum alloy 7075 subjected to different heat treatment processes during micro-cutting. Focusing on T6 and T73 heat-treated aluminum alloy 7075, the study employs a combination of experiments and simulations to analyze micro-cutting surface morphology, cutting forces, microstructure evolution, residual stress, and damage characteristics. The findings reveal that micro-cutting of aluminum alloy 7075 after T6 heat treatment exhibits no apparent speed sensitivity in the primary cutting force, while T73 heat treatment demonstrates noticeable speed sensitivity. The surface microscopic damage during micro-cutting is influenced by both cutting speed and depth, resulting in distinct forms and degrees of damage under varying conditions. An analysis of the residual compressive stress field indicates that the magnitude of residual compressive stress on the micro-cutting surface determines crack initiation, and the maximum depth of residual compressive stress dictates crack propagation. Microscopic damage in T6 heat-treated aluminum alloy 7075 predominantly occurs in the second and third deformation zones, while T73 heat treatment leads to most damage in the third deformation zone. Notably, crack propagation is evident in T6 heat treatment at any cutting speed with a cutting depth of 150 μm, whereas it is inconspicuous in T73 heat treatment at cutting speeds below 540 m/min. Furthermore, at cutting speeds below 540 m/min and a cutting depth of 150 μm, T6 heat-treated micro-cutting is prone to oxidative wear. In contrast, at a cutting speed of 72 m/min and a cutting depth of 150 μm, the predominant wear form in T73 heat-treated micro-cutting is oxidation wear. This study underscores the intricate interplay between heat treatment processes, cutting conditions, and microscopic damage in aluminum alloy 7075 micro-cutting. The nuanced insights provided contribute to a deeper understanding of the machining characteristics of this alloy, paving the way for improved processing methodologies.

Effect of Carburizing Temperature and Post Carburizing Treatments on Microhardness and Microstructural Evolution of Carburized Low-Carbon Steel

This paper reports the results of an experimental investigation of the effect of carburizing temperature and post carburizing heat treatments on the structural and hardness properties of pack carburized low-carbon steel. The carburizing processes were performed at temperatures of 900°C and 1035°C for 6 hours. After that, two hardening procedures were carried out. In the first hardening procedure, the specimens were directly quenched in oil from carburizing temperatures, while in the second procedure, a double quenching method using brine as a quenching medium was applied. The resultant changes in surface hardness values, carbon content, case depth, microhardness profiles, and microstructural evolution during all processes were tracked and reported. The study showed that the hardness values and carbon content of the carburized specimens increased significantly compared to an untreated specimen, also case depth values increased by two times in some hardened specimens, the increasing in these values were correlated to the changes in microstructures. The obtained results indicated that the structure and the properties of the carburized components are strongly influenced by carburizing temperature and by post carburizing heat treatments; therefore, both variables can be used to altering or modifying surface and core characteristics of the carburized steel, which make it more suitable for engineering components that require a combination of hard surface along with ductile and tough core.

Surface wear resistance and microstructure characteristic in longitudinal–torsional ultrasonic vibration side milling of GH4169 superalloy

The intrinsic link between the surface wear resistance and microstructural evolution of a material was revealed. The surface wear resistance of the GH4169 superalloy was systematically investigated in relation to the surface machining topography and mechanical properties at different cutting widths in conventional side milling (CSM) and longitudinal–torsional ultrasonic vibration side milling (LTUVSM). The wear resistance was evaluated by analyzing the wear topography, friction coefficient, duration of the initial wear stage (IWS), and wear volume of dry sliding wear. The specimens in LTUVSM exhibited higher wear resistance than those in CSM owing to the inhibition of friction and growth of inter-surface friction nodes by the uniform ultrasonic vibration texture (UVT) and the inhibition of subsurface crack nucleation and extension by the superior mechanical properties. The mechanism of the ultrasonic vibration intervention in grain refinement was revealed. The involvement of ultrasonic vibration enhanced the dislocation accumulation, the grain boundary fractures, and increased the recrystallization fraction, which resulted in a thorough grain refinement with a 7.3 % decrease in average grain diameter (AGD) relative to that obtained with CSM. The increased grain refinement in LTUVSM improved the mechanical properties of the surface-layer material, thereby improving the wear resistance of the specimen.

Surface and interfacial microstructure evolution of isothermally oxidized thermal barrier coating system

Novel multilayer functionally graded thermal barrier coating (TBC) system consisting of a newly developed glass-ceramic based bond coating, glass-ceramic-25% yttria stabilized zirconia (YSZ) composite coating and 100% 8-YSZ top coating. Since TBC is a layered system property matching between each layer is a major concern. Therefore, thermal properties of the developed glass-ceramic coating and composite coating were studied in detail. The developed system was exposed to static oxidation at 1100 °C for 100 h. To assess the efficacy of the TBC system, XRD phase analysis and also mechanical properties like Young's modulus and nanohardness was performed at each layer for both before and after isothermal oxidation. From the surface and interfacial microstructure evolution it was observed that there was crack development at composite coating-top coating interface, which was due to zirconia phase transformation from tetragonal to monoclinic crystal structure, confirmed by the presence of monoclinic zirconia XRD diffraction peaks in XRD analysis. Additionally, Raman spectroscopy was also carried out on the isothermally oxidized specimen, which also pointed out the presence of monoclinic crystal structure. Even though developed TBC system failed to protect the nimonic alloy (AE435) substrate from thermal exposure at 1100 °C for 100 h the glass-ceramic/substrate had a good interfacial adhesion. Main advantage of using glass-ceramic coating is its ability to tune coating properties by changing the composition. Thus, future works are being carried out to alter the glass-ceramic composition to develop a potential TBC system.

Measurement of the Diffusion Coefficient of Xenon in Self-Sintered Nanopore Graphite for Molten Salt Reactor

The economics and safety of reactors can be affected by the diffusion of fission products into graphite. Xenon (Xe) fission products diffusing into graphite is the most critical neutron absorber and poison that can slow down or stop the chain reaction. The transport parameters for inhibiting the xenon diffusion in graphite are therefore an important scientific problem. Self-sintered nanopore-isotropic (~40 nm) graphite (SSNG) derived from green pitch coke can decrease Xe diffusion into graphite. In this study, the surface morphology and microstructural evolution in graphite before and after irradiation, as well as after annealing, were studied with different characterization methods. A method for the measurement of diffusion coefficients of fission products’ diffusion in graphite using Rutherford backscattering spectrometry (RBS) was also reported. The SSNG substrates were implanted with Xe at a dose of 4.8 × 1015 ions/cm2 and energy of 7 MeV. The RT-implanted samples were annealed in a vacuum at 650 °C for 9 h. The implanted and annealed samples were characterized using RBS. The diffusion coefficient D (Xe, 650 °C) was 6.49 × 10−20 m2/s. The results indicate SSNG’s excellent ability to inhibit Xe diffusion and are significant for designing and evaluating the safety of nuclear reactors.

Rolling contact fatigue failure mechanism of bearing steel on different surface roughness levels under heavy load

It is inherent knowledge that rolling contact fatigue (RCF) failure of subsurface-initiated spalls usually occur under optimum surface under heavy load. However, our previous work has revealed surface-initiated RCF failure mechanism under heavy load and initial high roughness surface. The formation of surface crack caused by RCF is a complicated phenomenon that is accompanied by surface morphology and lubrication condition, as well as stress distribution and microstructure evolution. To clarify the main failure mechanism, this study carried out systematic RCF tests with different surface roughness specimens and conducted characterization of superficial microstructure for specimens of pre-service and post-service by Focused Ion Beam (FIB). The results clearly suggest precursor of collapsed morphology and nanocrystalline layer are the main factor that causes the RCF life with high roughness is lower than that with low roughness. While the spalling failure initiating from low roughness surface under heavy load are strongly relied on surface plastic deformation. Two main plastic deformation mechanisms are conductive to formation of surface cracks: the micro-plastic deformation and the local severe plastic flow. A newly failure mechanism that spalling failure initiates from surface has been proposed to link surface roughness and microstructure evolution.

Study on multi-field composite strengthening, surface integrity, and microstructural evolution mechanism of 7075-T6 aluminum alloy

Multi-energy field composite reinforcement technology has become a critical technique for improving the service life of key components in aviation engines. This paper aims to investigate the strengthening mechanism of high-speed cutting and solid particle-entrained waterjet peening (HSC-WJP) composite reinforcement on 7075-T6 aluminum alloy. Samples subjected to single solid particle-entrained waterjet peening (WJP) reinforcement were selected as the control group. The surface quality and microstructure evolution of 7075-T6 aluminum alloy after composite reinforcement were examined using SEM, EDS, XRD, TEM, and HRTEM techniques. The research results indicate that, under the same jet parameters, HSC-WJP composite reinforcement is superior to single WJP reinforcement in terms of surface roughness, except when the jet pressure is below 25 MPa and the track spacing is 0.53. The surfaces of the 7075-T6 aluminum alloy workpieces after reinforcement are mainly characterized by the presence of pits and micro-pores. Surface roughness shows a positive correlation with jet pressure and nozzle traverse speed. After HSC-WJP composite reinforcement, the surface roughness decreases by 0.132 μm compared to single WJP reinforcement, and the size of surface pits is reduced by 4–20 μm. Surface roughness decreases first, then increases, and then decreases again with increasing target distance, while it increases first and then decreases with increasing path spacing. A significant precipitation-free zone (PFZ) is present in the 7075-T6 aluminum alloy after reinforcement, and its width is positively correlated with the nozzle traverse speed. When the nozzle traverse speed is 120 mm/min, the average size of the PFZ at grain boundaries after single WJP reinforcement is 12–20 nm, while it decreases by approximately 3 nm after HSC-WJP composite reinforcement. The main precipitate phase in the reinforced aluminum matrix is η′ phase, and under the same jet parameters, the HSC-WJP grain size is smaller, approximately 25–34 nm, and exhibits significant dislocation walls and dislocation tangles, with a higher dislocation density compared to single WJP reinforcement.

Effect of Cyclic Loading on the Surface Microstructure Evolution in the Pearlitic Rail

The effects of cyclic loading on the surface microstructure evolution of different contact locations in a used pearlitic rail were studied. Microstructures were analyzed using Scanning Electron Microscopy (SEM). Meanwhile, grain boundaries and crystallographic orientations were explored via Electron Backscatter Diffraction (EBSD). At last, wheel–rail contact probabilities and forces were calculated using rail profiles. The results indicate that the side wear region located in the gauge face was 71.5% in the high-angle grain boundaries (HAGBs) fraction, 0.88 in the Kernel Average Misorientation (KAM) value, 36% in the recrystallization (REX) fraction, and had a predominant orientation in grains. The rolling contact fatigue (RCF) region situated at the gauge corner was 66.3% in the HAGBs fraction, 0.92 in the KAM value, 33% in the REX fraction, and was mis-orientated in grains. The region located at the edge of the running band was 60.7% in the low-angle grain boundaries (LAGBs) fraction, 0.97 in the KAM value, 12% in the REX fraction, and was mis-orientated in grains. Continuous dynamic recrystallization (cDRX) took place in wear and RCF regions during the cyclic rolling contact loading, creating ultra-fine grains with a transformation from LAGBs to HAGBs, lower KAM values, and more REX. Grains oriented along [111] parallel to the vertical direction in the wear region were influenced by the dominant normal force, while grains in the RCF region were non-oriented, which was attributed to large lateral and vertical forces of similar magnitudes.

Evolution of cold-expanded microstructure with aging temperature and its influence on fatigue performance of hole structure at elevated temperature

A surface-strengthened layer formed by cold expansion (CX) evolves at high temperatures. The evolution of surface integrity and microstructure after a CX-treated superalloy GH4169 center hole plate was investigated in the present study. Aging at 400 ℃ and 600 ℃ took place with a duration of 500 h (CX400 and CX600). In addition, the fatigue properties at 820 MPa/600 ℃/R= 0.1 were investigated. The results show that CX has a smooth surface, a compressive residual stress field with a depth of more than 1.4 mm and a non-improved surface hardness. The statistical fatigue life of the as-received specimens was 7015 cycles, and the fatigue lives after CX and CX400 treatment were 5.27 and 2.86 times higher, respectively, indicating an increase by CX and a decrease by 400 ℃ aging. In contrast, the fatigue life of the original sample decreased to 5576 cycles with 600 ℃ aging, while the corresponding fatigue life of the CX600-treated sample was 7979 cycles, representing a significant decrease in both cases. The transformation of the main strengthening γ″ phase to the δ-phase upon aging at 600 ℃/500 h are the main reasons for the weakening of the fatigue properties, which did not occur upon aging at 400 ℃ (see TEM).

Temperature dependence of surface microstructure of 316 L stainless steel exposed to low-energy hydrogen ion irradiation

The austenitic 316 L stainless steel (316LSS) is an important metal for nuclear installations due to its high strength, good plastic toughness and excellent corrosion resistance, and is commonly used as the plasma-facing and structural material. In this study, 316LSS samples are irradiated with low-energy hydrogen ions (35 eV) at the temperature of 400–1300 K to investigate the surface microstructure evolution. The experimental results show that the surface of 316LSS samples remains relatively smooth at 400 K and 600 K after irradiation. Significant surface roughening including spherical protrusions is formed on the surface at 800 K and 1100 K, and step-like streaks are observed at 1300 K. However, no drastic change in the surface morphology is observed in the separate annealing experiments at 800–1300 K. It has been shown that hydrogen ion irradiation mainly causes the surface microstructure evolution of 316LSS samples. After hydrogen plasma exposure, a large number of adatoms are first formed on the surface of 316LSS because of bubble growth. The adatoms then preferentially reach the defects by diffusion at certain temperatures, and aggregate into spherical protrusions with low surface energy. The qualitative simulation results show that the irradiation temperature affects the diffusion and aggregation of adatoms on the surface, and the radius of the spherical protrusions gradually increases due to the decrease of the surface binding energy and the increase of the irradiation fluence.

Improved resistance to chloride-induced corrosion through the combined influence of surface nanocrystallization and thermal oxidation treatments on AISI 321 stainless steel

This study comparatively examines the impact of combined surface nanocrystallization (SNC) and thermal oxidation (TO) treatments on the corrosion performance of AISI 321 austenitic stainless steel under chloride-induced conditions, highlighting their synergistic effects. To achieve this goal, the SNC process was first carried out using the high energy shot peening technique and then the TO treatment was performed by exposing the samples to Ar–21% O2 at 400 °C. The oxide films grown on both solution annealed (SAed) and the high energy shot peened (HESPed) samples show a double-layered structure: an inner Cr-rich and an outer-Fe rich layer. However, high density and uniform distribution of the crystallographic defects on the HESPed sample remarkably increased the Cr diffusion/flux throughout the oxidation front, and consequently a thicker Cr-rich inner oxide layer formed on the surface, as compared with the SAed one. A number of electrochemical examinations were conducted to investigate the corrosion behavior of oxidized and non-oxidized SAed and HESPed samples in 3.5 wt% NaCl solution. It was found that the oxidized HESPed sample shows the best corrosion performance with the highest values of critical pitting potential (+590 mV vs. Ag/AgCl) and charge transfer resistance (356.7 kΩ cm2). A physical model based on the surface microstructural evolution caused by the TO and SNC treatments and their synergistic effect on the formation of Cr-rich phases is provided.

Preparation of reactive urchin-like recycled concrete aggregate by wet carbonation: Towards improving the bonding capability of the interfacial transition zone in recycled aggregate concrete

To enhance the bonding capability between recycled concrete aggregate (RCA) and paste, an innovative carbonation method was developed to modify the surface characteristic of RCA by promoting the formation of needle-like aragonite using accelerated carbonation in Mg(NO3)2 solution under an elevated temperature (75 °C). The evolution of surface microstructure, phases and reaction kinetics was investigated using multiple testing methods including scanning electron microscopy, nanoindentation, X-ray diffraction, etc. The results revealed that reactive urchin-like RCA could be prepared within less than an hour after exposing to CO2. The urchin-like wrapping with a thickness of about 100 μm was seen rapidly grown on the surface of RCA, consisting of an outermost layer of aragonite coating, a thin layer of brucite and a silica-rich layer. The mineral wrapping induced by carbonation significantly modified the roughness, topography and geochemistry of RCA's surface entirely, contributing to enhanced bonding strength between RCA and new mortar (33.54%).

Effect of gas pressure on microstructure and mechanical properties of TC11 titanium alloy during supersonic fine particle bombardment

The surface nanocrystallization of a Ti–6.5Al–3.5Mo–1.5Zr–0.3Si (TC11) titanium alloy with a lamellar microstructure was carried out by supersonic fine particle bombardment (SFPB). The effect of SFPB gas pressure on its surface integrity, microstructural evolution and mechanical properties was systematically investigated. The results showed that gradient nanostructures on the surface of the TC11 alloy were successfully created after SFPB with different gas pressures. The grain size of the surface’s lamellar microstructure was completely refined to the nanometer scale. And the grain size of nanocrystals decreased with the increase of gas pressure. Meanwhile, the subsurface retained initial lamellar microstructure morphology. Surface roughness was minimized after SFPB with a gas pressure of 1.0 MPa, while microcrack formed at a higher gas pressure of 1.5 MPa, resulting in a decrease of compressive residual stress. With the increase of SFPB gas pressure, the surface microhardness and the depth of hardened layer gradually increased, and yield strength and tensile strength was improved. Nevertheless, the elongation was not greatly changed. The fracture morphology changed from typical ductile fracture to quasi-cleavage and ductile mixed fracture.