High Compressive Residual Stress Research Articles

Improving the high cycle fatigue property of Ti6Al4V ELI alloy by optimizing the surface integrity through electric pulse combined with ultrasonic surface rolling process

To improve the surface integrity and high cycle fatigue property of Ti6Al4V ELI alloy, the electric pulse has been introduced into the ultrasonic surface rolling process (USRP), which is called electric pulse-assisted ultrasonic surface rolling process (EUSRP). With the help of “electroplasticity” of the electric pulse, the thickness of the surface gradient deformation layer was about three times of the USRP specimens by adjusting the pulse current level. However, the surface hardness decreases due to the continuous effect of the pulse current and the “skin effect” during treatment. It is worth noting that the higher the applied pulse current, the more severe the softening. This paradox causes the fatigue performance of EUSRP specimens lower than that of USRP specimens. To break this paradox, the EUSRP treatment is followed by a USRP treatment. The EUSRP-2 (with a pulse current of 200 A) +USRP specimens exhibit excellent surface hardness, a gradient deformation layer thickness of about 400 µm, low surface roughness and high compressive residual compressive stress. Besides, the hardening mechanisms of the different surface strengthening specimens have been quantitatively analyzed in combination with microstructure analysis. The fatigue life of Ti6Al4V ELI alloy can be improved by about 25 times at 780 MPa using the EUSRP-2+USRP treatment, the main reason for the highest fatigue life is the deepest surface gradient layer and the deepest crack initiation site. The fatigue limit of the EUSRP-2+USRP specimens is not the highest because too much surface hardening causes compressive residual stress relaxation during cycling and the beneficial effect of compressive residual stress is eliminated.

Application of gradient severe shot peening as a novel mechanical surface treatment on fatigue behavior of additively manufactured AlSi10Mg

Post-processing methods can be crucial in addressing the associated anomalies of the as-built state of additively manufactured materials. In this study, for the first time, the effects of gradient severe shot peening as a novel mechanical surface treatment, along with other types of shot peening treatments, including conventional, severe, and over shot peening processes were investigated individually and combined with heat treatment on fatigue behavior of hourglass AlSi10Mg samples fabricated by laser powder bed fusion. Detailed experimental characterizations in terms of microstructure, porosity, surface texture, hardness and residual stresses as well as rotating bending fatigue behavior were conducted. The experimental results revealed a significant fatigue behavior improvement after applying gradient severe shot peening treatments due to their remarkable capacity to modulate surface texture, known as a side effect of peening, besides surface layer nanocrystallization, enhanced hardness, and high compressive residual stresses.

Characterization and optimization of weld properties due to the effect of different pin profiles for AA8011 – based friction stir welding

PurposeThis Friction stir welding study aims to weld thick AA8011 aluminium plates, and the interface joints created with a variety of tool pin profiles were examined for their effects on the welding process.Design/methodology/approachScanning electron microscopy and optical microscopy and X-ray diffraction were used to examine the macro and micro-structural characteristics, as well as the fracture surfaces, of tensile specimens. The mechanical properties (tensile, hardness tests) of the base metal and the welded specimens under a variety of situations being tested. Additionally, a fracture toughness test was used to analyse the resilience of the base metal and the best weldments to crack formation. Using a response surface methodology with a Box–Behnken design, the optimum values for the three key parameters (rotational speed, welding speed and tool pin profile) positively affecting the weld quality were established.FindingsThe results demonstrate that a defect-free junction can be obtained by using a cylindrical tool pin profile, increasing the rotational speed while decreasing the welding speeds. The high temperature and compressive residual stress generated during welding leads to the increase in grain size. The grain size of the welded zone for optimal conditions is significantly smaller and the hardness of the stir zone is higher than the other experimental run parameters.Originality/valueThe work focuses on the careful examination of microstructures behaviour under various tool pin profile responsible for the change in mechanical properties. The mathematical model generated using Taguchi approach and parameters was optimized by using multi-objectives response surface methodology techniques.

Investigation of Microstructural Characterization and Mechanical Properties of 8YSZ Thermal Barrier Coatings: Atmospheric Plasma Spray versus Electron Beam-Physical Vapour Deposition

In this study, the formation and growth of coating microstructure was studied and reported based on APS and EB-PVD deposition mechanism with the change in spray angle. A NiCrAlY bond coat with 8YSZ ceramic coat was applied by APS and EB-PVD deposition onto the Inconel 718 with the variation in spray angle. The investigation was divided into microstructural analysis and mechanical properties to determine the effect of different deposition mechanism and its variation in spray angle. The results obtained show that the APS with 60° spray angle has more presence of defects, followed by APS 90° and EB-PVD samples. The APS avg. grain size varies between ~ 400 to 800nm, whereas EB-PVD in between ~ 150 to 300nm. The EB-PVD with 90° spray angle results in low porosity i.e. 18.12 % followed by APS 90°, EB-PVD 60°, and APS 60° spray angle, respectively. The low porosity results in high compressive residual stress than medium and high porosity. The avg. Raman shift for EB-PVD 90° spray angle i.e. low porosity is 1.86 cm-1, for medium i.e. APS 90° and EB-PVD 60° is 1.33cm-1 and 1.53cm-1 respectively, and for high porosity is 0.93cm-1. The 90° spray angle showed better microstructural and mechanical properties compared to 60°.

Microstructure, mechanical properties and optical reflectance of TiNiN films deposited on silicon substrates using cathodic arc evaporation

Variations in applied substrate bias during cathodic arc deposition may impose intriguing consequences on the mechanical and optical properties of TiNiN coatings. Here, TiNiN films were fabricated onto Si substrates using a Ti95Ni5 (at.%) alloy target via cathodic arc evaporation employing a range of substrate bias voltages varying from 0 to -150 V. The aim of this study was to investigate the microstructures, mechanical performance, and optical properties of the TiNiN films in terms of the employed substrate potential. A significant enhancement (57%) in hardness for the TiNiN film was attained at -50 V as compared to zero substrate potential. This was principally attributed to the evolution of a fine, equiaxed nanocomposite structure, in association with the induction of a very high compressive residual stress at -50 V. In contrast, a maximum optical reflectance of 73% in the near-infrared range was determined for the coating synthesised at -150 V. It is speculated that incidence of fewer macroparticles on the film surface at elevated negative potentials, due to the induction of a higher repulsive force, may reduce the scattering of light incident on the coating's surface, promoting improved spectral reflectivity.

Effects of Laser Shock Peening on Corrosion Resistance of Additive Manufactured AlSi10Mg

Mechanical properties of Al alloys make them an ideal candidate for different sections of marine, aerospace, automotive, etc. industries. Recently taking the advantages of additive manufacturing (AM), many complex infrastructures/components can be fabricated with very high design freedom via Al alloys. Although Al alloys have good natural corrosion resistance, however improving this property attracts lots of attention in the past few years. Post-processing methods can play a key role for addressing the issues related to internal and surface anomalies associated with as-built AM parts. Generally, these anomalies have detrimental effects on mechanical properties. In the present study, the effect of laser shock peening (LSP) treatment with different laser pulse overlaps and energies was investigated comprehensively on microstructure, surface texture, porosity, hardness, residual stresses as well as corrosion resistance of laser powder bed fused (L-PBF) AlSi10Mg samples. LSP provides strain deformation on the surface, and the deformation enhances by laser beam energy. LSP1 (laser energy of 1.5 J and 50% overlap) and LSP3 (laser energy of 4.5 J and 50% overlap) introduce maximum local strain of 7.5 and 10.7, respectively. The surface roughness of as-built state µm in terms of Rv was effectively diminished to 16.33 after LSP6 (laser energy of 4.5 J and 75% overlap). The results indicated that due to the modified surface texture, improved hardness and induced high compressive residual stresses in the surface layer. (surface hardness improvement and inducing high surface compressive residual stresses were obtained after LSP6 up to 26% and −289 MPa, respectively); the LSP treated samples exhibited higher corrosion resistance with the corrosion rate decreasing down to 50% as compared to the as-built state.

New displacement-based finite element analysis method for predicting the surface residual stress generated by ultrasonic nanocrystal surface modification

Peening techniques can be applied to relieve high tensile residual stress, which is one of the main causes of primary water stress corrosion cracking (PWSCC). Ultrasonic nanocrystal surface modification (UNSM) is a peening technique that generates a high compressive residual stress on the surface of a structure. Finite element (FE) analysis can be utilized for quantitative surface stress prediction according to the UNSM in various materials and loading conditions. In this paper, a new method to predict the surface residual stress generated by UNSM process through FE analysis is proposed. In order to accurately simulate the UNSM process through FE analysis, it is necessary to define an equivalent displacement calculation method that can replace the complex load states of UNSM. For this, we proposed the new equivalent displacement calculation method based on the contact mechanics theory and the energy conservation law. The new equivalent displacement calculation method was validated by comparing the indentation depth obtained by single-path UNSM FE analyses and experiments under various loading conditions. The actual UNSM process is carried out in multiple paths over a large area of the structure. By applying the new equivalent displacement calculation method, the compressive residual stresses were calculated through multi-path UNSM FE analyses and compared with the results obtained from the multi-path UNSM experiments. The surface residual stress results of the experiments and analyses showed good agreement, and it was confirmed that the UNSM process can be simulated well if the new equivalent displacement calculation method is used for the FE analysis.

Experimental investigation on creep strengthening phenomenon of a Ni-based single crystal superalloy under cyclic loading and unloading conditions

The complex failure behavior of turbine blades under cyclic creep is of great significance to the safety of aeroengines. In this study, the deformation regulation and fracture mechanism of a single-crystal Ni-based superalloy DD6 under cyclic loading at 980 ℃ are investigated, and the strengthened rupture life and fracture deformation are clearly exhibited. Scanning electron microscopy and electron backscatter diffraction observations were conducted to reveal the deformation and fracture mechanisms. A smaller particle spacing of the γ/γ’ interface was observed under cyclic loading/unloading, which restricted dislocation movement and reduced the creep rate. This led to an extended creep life of steady creep stage, and the delay of the accelerated creep stage. Additionally, the creep deformation distribution and slip system activation affected the fracture toughness under the accelerated creep stage, leading to an increase in the creep fracture strain under cyclic loading/unloading. Finally, the fracture mechanism affected by cyclic loading is discussed based on inner and surface cracks. Cyclic loading/unloading promotes the multisource initiation of surface cracks, which improves loading capacity. Furthermore, cyclic loading/unloading promotes the generation of secondary cracks deflected from crack tips. The high residual compressive stress at the crack tip delays creep-crack initiation during unloading, leading to a decrease in the creep-crack propagation rate. These factors led to cyclic strengthening at different scales.

Effect of high-speed ultrasonic vibration cutting on the microstructure, surface integrity, and wear behavior of titanium alloy

Titanium alloys are widely used in aviation, marine, automotive, offshore, and medical fields. However, their poor wear resistance reduces the safety and reliability of components during service. Few study has been previously conducted on the wear resistance enhancement of titanium alloys (including Ti–6Al–4V alloy) processed by mechanical cutting. High-speed ultrasonic vibration cutting (HUVC) is an effective approach for improving the machinability of titanium alloys. In this study, we attempted to utilize HUVC improving the wear resistance of titanium alloys. After conducting high-speed turning (cutting speed within the range of 200–300 m/min), the surface integrities (surface roughness, microstructure, in-depth micro-hardness, and residual stress) of conventional cutting (CC)- and HUVC-machined samples were characterized. Experimental results demonstrated that, compared with CC, HUVC achieved a thicker plastic deformation layer (greater than 46.93 μm), lower surface roughness, higher surface micro-hardness (greater than 433 HV0.05), and higher compressive residual stress (up to −840 MPa). Moreover, surface nanocrystallization and gradient nanostructured layer were observed in HUVC-machined Ti–6Al–4V samples. In addition, compared with CC, HUVC effectively further reduced the friction coefficient and worn volume loss (decreased by 20.98%–25.59%) and ultimately improved the wear resistance. The hardness has a higher influence on the wear resistance of the machined Ti–6Al–4V alloy than the other surface integrity factors. Therefore, the proposed mechanical cutting operation was confirmed to improve the wear resistance of titanium alloys.

Experimental investigation on the spalling failure of a railway turnout made from Hadfield steel

In a rail track structure, a turnout is used as a transition between straight and branching rails and therefore withstands complex dynamic rolling and impact loading. This paper reports a comprehensive failure investigation of a railway off-track turnout made from Hadfield austenitic cast steel. The worn turnout was examined using optical microscopy, scanning electron microscopy, micro-hardness, and quantitative X-ray diffraction analyses. A ball-on-disc sliding wear test was also applied to evaluate the impact of work-hardening on the wear property. The turnout exhibited surface embrittlement, severe cracking, delamination, and spalling characteristics. Severe plastic deformation of the worn turnout was observed with the formation of densely packed mechanical twins, which facilitated crack propagation. The rail top developed a gradient hardness (HV0.1) profile from the rail top of 8.9 GPa, the cracked subsurface of 5.9 GPa to the bulk steel of 2 GPa. The rail top was also found to have accumulated an extremely high residual compressive stress of 500–650 MPa. Strain induced martensite transformation was repeatedly evidenced by X-ray diffraction peak of the ferritic (110) plane although the highly strained and nanocrystallised ferrite was only detected on the severely deformed rail top. Comparative sliding wear tests showed highly deteriorated wear resistance of the strain-hardened rail top as compared to the bulk steel.

Effect of shot peening and nitrogen ion implantation on the fatigue behavior of TA15 titanium alloys

The titanium alloy TA15 was treated with SP (shot peening), followed by heat exposure at 500 °C and NII (nitrogen ion implantation) treatment at 500 °C for 5 h each. The surface topography, microstructure, micro-hardness, residual stress, and fatigue behavior were, thereafter, analyzed. The results showed that the SP and NII treatments changed the surface topography of the TA15 titanium alloy, producing a high density dislocation and a high amplitude residual compressive stress on its TA15 titanium surface. In addition, the local stress concentration on the surface was reduced, pushing the fatigue nucleation site below the surface. Also, the difficulty of crack initiation and propagation was increased. At 450 MPa, the fatigue life of the SP treated sample was increased by 23.5 times. A large amount of TiN was generated in the grains of the NII treated sample, and compared with a sample without any NII treatments, the median fatigue life was increased by 17 times. The results showed that SP can effectively improve the fatigue properties of a TA15 titanium alloy, and the NII treatment is an effective way to improve the thermal stability of the SP strengthening effect.

Numerical study on local residual stresses induced by high frequency mechanical impact post-weld treatment using the optimized displacement-controlled simulation method

The High Frequency Mechanical Impact (HFMI) treatment is a reliable, effective, and user-friendly post-weld technique for fatigue life enhancement of welded structures. The working principle for HFMI can be characterized by impacts from cylindrical indenters with a high frequency which introduces the local work hardening and high compressive residual stresses (RS) and reduces the stress concentration at the weld toe. These beneficial effects are needed to be considered in the fatigue assessment and design of those HFMI-treated structures. This study proposes a multi-process numerical simulation model to estimate local RS and improved shape profiles induced by HFMI treatment in welded joints. Firstly, the welding simulation is performed by thermal-elastic-plastic finite element (TEPFE) analysis using a coarse finite element (FE) mesh model. The zooming technique is then applied to transfer simulated as-welded RS to the ultra-fine mesh used in HFMI analysis as initial stresses. Finally, the numerical analysis of HFMI-induced RS is carried out using the optimized displacement-controlled numerical simulation method. An HFMI-treated out-of-plate gusset welded joint specimen was fabricated using SM490 steel. The surface topography for the treated zone, RS before and after the HFMI process, and thermal cycles during the welding process were experimentally investigated to calibrate and validate the proposed simulation approach. Both simulated local deformed shape profiles and RS were in good agreement with the measurements. In this paper, the recommendations for FE modeling and the procedures for determining HFMI analysis parameters were discussed in detail.

Effects of deposition temperature on the wear behavior and material properties of plasma enhanced atomic layer deposition (PEALD) titanium vanadium nitride thin films

This work investigates the effects of deposition temperature on the wear behavior and material properties of recently developed plasma enhanced atomic layer deposited (PEALD) TiVN films. ∼50–100 nm thick TixV1-xN (x ~ 0.5, hereto referred to as TiVN) films were deposited using PEALD on Si substrates with thermal oxide at a range of deposition temperatures (150 °C, 200 °C, 250 °C, 300 °C, 350 °C). Wear testing was performed on each film using a linearly reciprocating tribometer in a controlled humidity environment. Wear rates of the TiVN films varied with deposition temperature, with the 250 °C sample achieving ultralow wear(5.4 × 10−7 mm3/Nm), while the 150 °C sample wore through the film completely in early sliding cycles. Along with their low wear properties, these PEALD TiVN films were found to have low electrical resistivity when deposited above 150 °C. Film density and crystallite size increased with increasing deposition temperature up to 250 °C, where these properties plateaued. High compressive residual stresses were measured, ranging from 2.7 to 7.7 GPa. XRD Bragg peak intensities showed that films with increasing deposition temperatures had higher degrees of crystallinity. XPS indicated that above 150 °C deposition temperatures, impurities in the film were reduced by ∼4x. Higher deposition temperatures allow for increased adatom mobility, which can lead to higher densities and crystallinity, which are typically associated with lower wear rates. At deposition temperatures below 200 °C, precursor reactivity is sluggish and there is insufficient energy for complete surface reactions to occur, leading to film contamination and less dense films. The subtle differences in wear rates above 200 °C deposition temperature indicated that there are competing material properties that can either contribute to or detract from the wear behavior of the film, and a combination of desirable mechanical, physical, structural, and chemical properties are required for ultra-low wear rates to be achieved. The low wear and friction properties and low electrical resistivity of these films combined with the low deposition temperature, conformality, and atomic layer thickness control of PEALD make them potential candidates for applications such as thermally sensitive microelectronics and MEMS/NEMS.

Effect of carburizing process on bending fatigue performance of notched parts of 18CrNiMo7-6 alloy steel

Since stress concentration is easily formed at the notch, improving the fatigue performance of notched parts is critical. The carburizing process is widely used to manufacture notched parts. In this research, the effects of carburizing process and notch stress concentration on fatigue performance were analyzed by bending fatigue tests. In addition, the microstructure and hardness evolution processes of the carburized notched 18CrNiMo7-6 specimens were observed quasi-in situ. The results showed that macro-plasticity has little effect on the bending fatigue performance of notched samples and that the improvement in fatigue performance is primarily attributable to the high hardness and residual compressive stress introduced by carburizing. The fatigue notch sensitivity is therefore reduced after carburizing. Compared to the uncarburized specimens, the fatigue limit of the carburized specimens is increased by up to 128%. With the increase of the effective hardening layer depth, the fatigue limit increases first and then decreases. Moreover, the brittle phase transformation product (twinning martensite) of metastable retained austenite is easy to produce stress concentration. Conversely, the 'film-like' retained austenite with an extremely high stability can effectively avoid the phase transformation products.

Microstructure and Mechanical Properties of TiN/Ti2AlN Multilayers

Titanium nitride (TiN) thin films deposited by high-power pulsed magnetron sputtering usually have a high compressive residual stress, which is not conducive for the adherence of TiN thin films. This study investigated the potential of Ti2AlN for releasing the compressive residual stress of HPPMS-deposited TiN thin films and evaluated the adherence strength and hardness of TiN/Ti2AlN multilayers by introducing the Ti2AlN MAX phase to form TiN/Ti2AlN multilayers. The results showed that smooth TiN/Ti2AlN multilayers with the TiN (111) and Ti2AlN (002) textures were successfully synthesized by HPPMS deposition and subsequent vacuum annealing. The compressive residual stress in TiN was released by Ti2AlN. The adherence strength of the TiN/Ti2AlN multilayers was improved after the release of the compressive residual stress, and the hardness of TiN/Ti2AlN multilayers was close to the annealed TiN. This study provides a novel approach for releasing the residual stress of hard ceramic thin films using the MAX phase.

Effect of Diamond Burnishing on the Properties of FSW Joints of EN AW-2024 Aluminum Alloys

The article presents the results of an analysis of the surface roughness parameters, microhardness, and the stresses of the surface layer ofFSW butt joints subjected to the burnishing process with a diamond tip. This can be useful in selecting the optimal parameters of the burnishing process, ensuring the best properties of the surface layer of the FSW joint. Burnishing force and feed rate influence were analyzed according to the two-factor three-level full factorial statistical completed plan PS/DC 32. The tested material was 2024-T3 aluminum alloy sheets with a thickness of 2 mm. The results show that burnishing significantly reduced the surface roughness from Sa = 6.46 μm to Sa in the range of 0.33 μm–1.7 μm. This treatment provides high compressive residual stresses σx from −86 to −130 MPa and σy from −158 to −242 MPa. Microhardness increased from 84.19% to 174.53% compared to butt joints. Based on the obtained results, multi-criteria optimization was carried out. This optimization allows us to obtain a compromise solution ensuring compressive stresses in the surface layer (σx=−123 MPa and σy=−202 MPa) and microhardness HV=362.56 mm/mm2 with the roughness of the weld surface Sa = 0.28 µm, Sku = 3.93 and Spc = 35.88 1/mm.

The effect of laser texture on adhesion and tribological properties of boron-doped diamond film on WC-Co cemented carbide

The mismatch between the coefficients of thermal expansion of diamond and WC-Co cemented carbide causes hot filament chemical vapor deposition 1 1 HFCVD (HFCVD) diamond film tools to be prone to film flaking and wear, which severely limits their promotion in the field of ultra-precision machining. The aim of this paper is to investigate the effect of different texture on the adhesion and friction properties of boron-doped diamond 2 2 BD (BD) film. Processing of different types and depth-diameter ratio of textures on carbide surfaces by laser technology and deposition of BD films by HFCVD method. The microstructure of films was characterized, the adhesion strength and friction properties of films were study by indentation and friction tests. The results show that texture with 15 % depth-diameter ratio facilitates the growth of diamond in (111) crystal face orientation and inhibits the production of non-diamond carbon in the sp2 structure, and the secondary nucleation rate of diamond in texture edge is higher. The compressive stress at the edge of the texture with 15 % depth-diameter ratio is greater, resulting in stronger adhesion of the film. Under dry friction environment, serrated texture has a lower coefficient of friction and wear rate than grooved texture due to its excellent chip storage capacity. However, the depth-diameter ratio should not be too large, grooved texture with 30 % depth-diameter ratio will reduce the friction performance and adhesion of BD film. Therefore, the adhesion and tribological properties of BD film can be improved by changing the texture type and the depth-diameter ratio, of which the effect of the depth-diameter ratio is more significant. • Secondary nucleation rate is higher at the texture edge. • Higher compressive residual stress and adhesion at the edge of texture • Texture depth-diameter ratio has great influence on the properties of diamond film. • The prepared tools show the common advantages of combining textured and film tools.

Defect suppression and grain refinement during ultrasonic vibration-assisted side milling of GH4169 superalloy

In order to suppress the axial vibration stripes machining defects (AVSMD) and achieve the engineering goal of multi-demand high quality processing with grain refinement during side milling of GH4169 superalloy, the defect formation mechanism in conventional side milling (CSM) and the defect suppression mechanism in ultrasonic vibration-assisted side milling (UVASM) have been investigated respectively. The impact of ultrasonic high-frequency energy field on subsurface grain refinement was also investigated intensively. The results show that the axial vibration stripes width proportion factor (AVSWPF) in UVASM was quantitatively and numerically smaller than the AVSWPF in CSM. Furthermore, the mechanism of machining defect suppression in UVASM was fully analyzed with three aspects. Compared to CSM, the frequency fraction of small diameter grains (3.51 μm) and the average grain diameter in UVASM were respectively reduced by 26.2 % and 10.7 % due to the continuous intervention of ultrasonic high-frequency energy impact. The finer grains and higher residual compressive stress can be achieved in UVASM, thus improving the wear resistance, strength, and fatigue life of the material to some extent. The results show that defect suppression and grain refinement can be achieved simultaneously in UVASM processing, which has great research value for the formability processing of series superalloys.

Microstructure and residual stress modulation of 7075 aluminum alloy for improving fatigue performance by laser shock peening

Laser shock peening (LSP) is an advanced surface-strengthening technology that improves the anti-fatigue performance of metallic components. However, there is a significant barrier to the application of thin-walled components because the high-energy laser causes deformation and nonuniformity of compressive residual stress, thereby reducing fatigue performance. In this study, an LSP technology based on a low-pulse-energy laser was developed. We applied it to a thin-walled AA7075 aluminium alloy specimen (∼4 mm thickness) and achieved an improvement in the high-cycle fatigue limit of 20.4 and 37.0% for the smooth and pre-cracked fatigue specimens, respectively, in the absence of deformation. It was discovered that the enhanced dynamic nanoscale precipitation and dislocation multiplication effects of the high-pressure shock wave contribute to microstructure stability under cyclic loading, resulting in high compressive residual stress stability. Moreover, the unique heterogeneous grain structure on the surface layer subjected to LSP at low pulse energy effectively restrains crack initiation and propagation. Because these findings apply to a wide range of alloys, the current results create new avenues for improving the fatigue performance of thin-walled components.

Laser assisted cold spray of 15–5 PH stainless steel in a designed and developed setup

Laser Assisted Cold Spray (LACS), a hybrid deposition process can be used to deposit crack free coatings in solid state with high compressive residual stress for variety of materials. However, high gas consumption rate, high maintenance cost, and costly experimental set-up often restricts its widespread usage in industries. The present work attempts to address these challenges. A novel design for a compact supersonic nozzle has been conceptualized and fabricated. The nozzle is designed for 2 Mach gas velocity having Converging- Diverging- Barrel (C-D-B) typed shape in which powders are injected in the barrel zone where the gas pressure ratio is minimum. Thus, it can be used with any commercially available low gas pressure powder feeder. The flow characteristics of the gas jet coming out of the nozzle have been characterized using a simple yet accurate home-built experimental setup. Gas velocity measured at the 5 mm standoff distance was ∼ 550 m/s, which compared well with the supersonic gas velocity estimated by measuring the gas jet temperature at the nozzle exit. Crack-free deposition of 15–5 PH Stainless Steel up to 220 µm layer thickness and an average compressive residual stress of 372 MPa was obtained on SS304 substrate. Substantial increase in hardness and scratch hardness,1.5 times and 2.5 times respectively, of the coating was obtained as compared to those of the substrate material. The coating could sustain upto 60 N load without producing any cracks during scratch test.