Surface Yield Strength Research Articles

The effect of laser shock peening with different power density on the microstructure evolution and mechanical properties of MAR-M247 nickel-base alloy

This study investigates the effects of laser shock peening (LSP) on the microstructural evolution and surface hardening of MAR-M247 nickel-based alloy. Experimental and numerical simulation methods are employed to analyze the influence of pulse power density and spot size. The results demonstrate that LSP significantly enhances surface hardness and yield strength. As the pulse power density increases, the magnitude and depth of plastic deformation increase. Higher power densities can implant deeper and greater compressive residual stress (CRS), but the corresponding tensile residual stress (TRS) also increases. Reducing both power density and spot size decreases the amount of plastic deformation of the surface. However, decreasing the spot size results in a decrease in the depth of the CRS. On the other side, based on the analysis of the microstructure, during the process of LSP, many dislocations accumulate in the γ matrix and evolve into subgrain boundaries, resulting in grain refinement. Additionally, LSP induces the precipitation of nanoscale carbides. This study tries to establish the influence law and action mechanism between LSP process-material property-microscopic evolution, which provides theoretical and applied data support for engineering applications.

Metamorphic layer properties with gradient microstructure distribution of 8Cr4Mo4V steel by grinding

In the grinding process, the metamorphic layer difference from the workpiece material is created on the grinding top surface, and its properties can greatly affect the bearing surface yield strength. In this study, the phase content and grain size distribution of 8Cr4Mo4V with the metamorphic layer were detected using advanced surface observation tools, and the influence of grinding process parameters on the microstructure of the metamorphic layer was considered at the same time. In addition, based on the modeling of the observed metamorphic layer with gradient microstructure distribution, tensile simulations of the metamorphic layer were performed by the crystal plasticity finite element method to investigate the effects of different grain size, phase content, and surface texture strength on its mechanical property like yield strength. Furthermore, the yield strength of the metamorphic layer was characterized by the nanoindentation technique. Finally, it was found that the grinding process parameters affected the microstructure and distribution of the metamorphic layer and thus changed its yield strength, and this study which combines the experiment and simulation aimed to quantitatively analyze the influence of different microstructures on the metamorphic layer.

Effect of surface stress concentration control and surface material strengthening on the fatigue performance of shot-peened single-crystal superalloy

This study analyzes the effect of shot peening on the surface integrity of nickel-based single crystal superalloys (SX) and the evolution of stress concentration factors caused by surface finishing and casting micropores near the surface before and after shot peening by numerical simulation. On one hand, SX forms a surface gradient plastic deformation structure after shot peening. The surface yield strength is 82% higher than that of the matrix by nanoindentation fitting. The deformation of the surrounding materials of the near-surface casting micropores is significantly greater than that of the materials at the same depth by EBSD. On the other hand, the series parameters of surface roughness after shot peening are higher than those of grinding. However, the stress concentration Kt1.32 at the bottom of the smooth crater is significantly lower than that of grinding "furrow" Kt1.94. The surface gradient deformation caused by shot peening flattens the surface casting micropores so that the stress concentration at the upper end of the micropores is significantly smaller than that in the grinding state. Based on the above two effects, the rotary bending fatigue limit of the single crystal alloy after shot peening at 650 °C is increased by 13.0% compared with the ground state. The peened sample no longer originates from the casting micropores.

Experimental Study on FGH95 Superalloy Turbine Disk Joint Material by Oblique Laser Shock Processing

The FGH95 superalloy used for turbine disk manufacturing was strengthened by the oblique laser shock processing (OLSP). The laser energy, beam diameter, and number of impacts were selected as the test factors, and the three-factor three-level oblique laser shock processing orthogonal test was carried out. Based on the analysis of variance and range of the surface residual stress, microhardness, roughness, tensile strength, and yield strength of FGH95 superalloy after LSP, the factor level combination of relative best comprehensive performance was obtained. The results showed that, within the 10% confidence level, the order of influencing factors with significant difference is: laser energy > number of impacts > beam diameter. Compared with the unimpacted sample, the microhardness of the material surface was increased by about 25% after OLSP. With the increase of laser energy, the dimple distribution of the sample was more uniform, smaller in size, and shallower in depth. However, the thickness of the affected layer was very low, and there was no significant effect on the tensile properties. In general, and under the test conditions selected in this study, the combination of 8 Joule laser energy, 3 mm beam diameter, and three impacts can be selected to obtain the best comprehensive performance. The results of this paper provide a reference for the OLSP of the FGH95 superalloy turbine disk and other aero engine parts.

Microstructural evolution and mechanical properties of Cu-based alloy by post-sintering ultrasonic nanocrystal surface modification

In this study, an ultrasonic nanocrystal surface modification (UNSM) was used to enhance mechanical properties of CuSn10Pb10 alloy. Top surface coarse grains were refined into nano-grains (mean size of 45–74 nm) after UNSM. Mechanical testing results revealed that the surface hardness, yield strength and ultimate tensile strength increased after UNSM owing to the formation of nano-grains containing some nano-twins that can be elucidated according to the Hall-Petch relationship. Grain size refinement mechanism was attributed to the increase in dislocation density and the formation of new dislocations, where the accumulation of them at low-angle grain boundaries caused a variation of the grain orientation.

Investigating the Effect of Electrical Discharge Process Input Parameters on Mechanical Properties of Aluminum Surface

One of the important parameters in electrical discharge machining is the presence of micro cracks on the workpiece surface (recast layer). Therefore, the aim of this study was to investigate the possibility of increasing the mechanical properties of aluminum surface by alloying elements (copper and nickel) diffusion to the recast layer and thus removing surface micro cracks. For this purpose, pulse on time and pulse current in with and without ultrasonic vibration have been considered as input parameters and the presence of surface micro cracks has been investigated using microscopic images. Also, the yield stress of the surface layer was calculated using the surface micro hardness. Based on the obtain results, surface without micro cracks has been created on the aluminum surface due to the diffusion of copper and nickel into the workpiece surface which increased aluminum surface yield strength from 90MPa to 280MPa without ultrasonic vibrations and to 310MPa while applying ultrasonic vibrations. In other words, ultrasonic vibrations cause an average of 20% increase in surface layer yield strength. In addition, according to the wear test, in the case of using ultrasonic vibration, improving the mechanical properties of the surface has caused thinner grooves on the aluminum surface.

Hierarchical‐Porous Copper Foams by a Combination of Sponge Replication and Freezing Techniques

Open‐porous copper foams with additional strut porosity are manufactured by two different manufacturing routes. The first is based on the Schwarzwalder sponge replication technique. The second method is a combination of Schwartzwalder sponge replication and freezing technique in which an additional strut porosity is generated inside the struts of the sponge‐replicated foams by freezing at −20 °C for 24 h and subsequent sublimation. Thermal processing of both types of foams is conducted at 500 and 900 °C for 6 h in a hydrogen‐containing atmosphere to reduce copper oxides and to facilitate the sintering process of the copper powder particles. Despite significant shrinkage of both foam series after thermal processing, hollow struts and lamellar pores keep their shape and do not collapse. The influences of the additional lamellar pores and thermal processing temperature on the cellular structure, porosity, specific surface area, yield strength, absorbed energy, and thermal conductivity are studied. The additional strut porosity generated by the freezing step significantly increases the specific surface area of the copper foams by a factor of 2 in comparison to the sponge replicated foams.

Preparation and tribological properties of PTFE/DE/ATF6 composites with self-contained solid-liquid synergetic lubricating performance

A new kind of PTFE composite with self-contained solid-liquid synergetic lubricating effect is prepared by the combination of PTFE, porous diatomite (DE), and immersed lubricating oil (ATF6). The tribological and mechanical properties of composites with different DE contents and varying cold-pressed pressures were investigated systematically. Due to the oil storage effect of DE particles, the maximum oil content of PTFE/DE composite is 16.4 wt%. With the increase of DE content, the surface hardness, elastic modulus and yield strength can be increased from 3.2 to 3.6 HV, 37.8–60.2 MPa and 8.7 MPa–12.8 MPa, respectively. With the addition of DE, the wear rate of PTFE decreases but the coefficient of friction (COF) increases. Meanwhile, with the addition of DE and ATF6, both the COF and wear rate of PTFE decrease. The COF can be reduced by 68% from 0.121 (specimen 0%-10 MPa-dry) to the minimum value of 0.039 (composite 10%-10 MPa-ATF6), and the wear rate can be reduced by 82% from 1.95 × 10−4 mm/Nm (0%-50 MPa-dry) to the minimum value of 0.35 × 10−4 mm/Nm (10%-50 MPa-ATF6). The enhanced antifriction performance of the composite PTFE/DE/ATF6 is contributed by the synergistic lubricating effect of self-contained liquid lubricant of ATF6 and the solid lubricant of PTFE. The prepared PTFE/DE/ATF6 composites exhibit excellent tribological performance as well as the mechanical properties, which can be used to fabricate a new kind of self-lubricating materials with high performance and long durability.

Determination of surface mechanical property and residual stress stability for shot-peened SAF2507 duplex stainless steel by in situ X-ray diffraction stress analysis

In this study, SAF2507 duplex (austenite–ferrite) stainless steel was processed by shot peening. The depth–profile variations of the stress state and work hardening in the shot-peened layer were investigated by X-ray diffraction and microhardness tests. The evolutions of surface morphology and microstructure were investigated using scanning and transmission electron microscopy. The stress–strain relations of the shot-peened surface and surface residual stress relaxation caused by cyclic stresses were experimentally determined by in situ X-ray diffraction stress analysis combined with tensile tests. Results showed that shot peening (SP) has induced severe plastic deformation in the surface layer, with the attendant work hardening and high compressive residual stresses (CRS). Nevertheless, there were incompatibilities in plastic deformation between the phases, and more property improvements represented by higher CRS, peak breadth and microhardness were conferred into austenitic phases. SP notably enhanced the surface yield strength of this two-phase alloy. The surface yield strength σ0.2 of ferrite and austenite were around 780 and 1100MPa after SP, which were 59% and 104% respectively higher than that of the untreated surface. The surface stress relaxation under cyclic tensile loadings consisted of a two-stage process. The surface residual stresses relaxed dramatically within the first cycle (N=1), then decreased linearly with the logarithm of loading cycles (N>1). The more severely deformed microstructures in austenite resulted in higher surface yield strength and contributed to higher cyclic stability of residual stress.

Time-Dependent Reliability Analysis of Corroded Steel Beam

The time-dependent reliability of corroded steel beam was investigated. Nine groups of specimens were subjected to accelerate corrosion by the outdoor periodic spray test and monotonic tensile test. The surface profile of corroded steel plates and the 3D data of corrosion depth were measured by the three-dimensional non-contact surface topography instrument (PS50 3D). The probability distribution of corrosion depth and nominal yield strength of corroded steel plates were studied. Finally, a probabilistic limit state equation for corroded steel beams was established and the time-dependent failure probability and reliability index of corroded steel beams was calculated by Monte Carlo simulation method (MCS). The results of study show that the corrosion depth on steel plate surface and nominal yield strength of corroded steel plate conformed to the normal distribution. With the increase of corrosion time, the average, the standard deviation of the corrosion depth and relative yield strength increased while the mean of relative yield strength, nominal yield strength, nominal ultimate strength, the elongation decreased. The reliability index decreased rapidly with corrosion time, which shows that the reliability of steel structures under the aggressive environmental should be caused attention.

Growth, Linear and Nonlinear Optical Studies of D-Tartaric Acid Crystal

A single crystal of D-Tartaric acid, a stereoisomer of tartaric acid, has been grown by a slow solvent evaporation technique. Good crystals to be used for optical testing were harvested after multiple recrystallizations, whose maximum size is 30x20x4mm 3 . In view of finding second harmonic generation efficiency and properties supporting for a nonlinear optical device, the grown crystals were subjected to various characterizations. Firstly, the compound was confirmed by single crystal and powder X-ray diffraction analysis and thereafter further studies were undertaken. Various possible functional groups available in the grown crystalline compound were identified using Fourier transform infrared analysis and reported. The second harmonic generation, a nonlinear optical property of a crystal, was studied and compared with standard KDP crystal. The percentage of linear optical transmittance in the ultraviolet, visible and infrared radiation of wavelength ranging from 200 to 1100 nm was studied and explained in detail. Thermal studies such as Thermogravimetric and Differential thermal analysis were carried out to find the thermal stability of the crystalline material. Vicker’s microhardness testing was made on the as-grown crystalline surface to find the surface hardness, yield strength and other related mechanical properties of the crystal. Copyright © VBRI Press.

Numerical study on residual stress redistribution of shot-peened aluminum 7075-T6 under fretting loading

This study attempts to analyze the residual stress redistribution under fretting loading by using FEM. The FE analysis model used in this study considers the variation of surface yield strength, the evolution of contact surface profile and the variable friction coefficient. The initial residual stress of shot-peened specimen is measured by X-ray diffraction method. Nano-indentation experiment is conducted to measure the yield strength of material surface layer. Pin-on-plate wear experiment is used to measure the wear coefficient of shot-peened aluminum 7075-T6. A fretting experiment is designed to measure the friction coefficient and verify the FE analysis model. The results show that the relaxation of residual stress is more likely to occur near the trailing edge of contact area, and the specimen with higher shot peening intensity undergoes the larger residual stress relaxation. In addition, the residual stress near the contact center region increases with the increase of loading cycles due to the fretting wear.

Semi-Empirical Modelling of Erosion Phenomena for Ice Crystal Icing Numerical Simulation

<div class="section abstract"><div class="htmlview paragraph">The aim of this work is to develop a semi-empirical model for erosion phenomena under ice crystal condition, which is one of the major phenomena for ice crystal accretion. Such a model would be able to calculate the erosion rate caused by impinging ice crystals on accreted ice layer.</div><div class="htmlview paragraph">This model is based on Finnie [<span class="xref">1</span>] and Bitter [<span class="xref">2</span>] [<span class="xref">3</span>] solid/solid collision theory which assumes that metal erosion due to sand impingement is driven by two phenomena: cutting wear and deformation wear. These two phenomena are strongly dependent on the particle density, velocity and shape, as well as on the surface physical properties such as Young modulus, Poisson ratio, surface yield strength and hardness. Moreover, cutting wear is mostly driven by tangential velocity and is more effective for ductile eroded body, whereas deformation wear is driven by normal velocity and is more effective for brittle eroded body. Several researchers based their erosion modelling on these two phenomena such as Hutchings et al. [<span class="xref">4</span>] for deformation erosion, or Huang et al. [<span class="xref">5</span>] and Arabnejad et al. [<span class="xref">6</span>] for cutting and deformation erosion.</div><div class="htmlview paragraph">The main work of this paper is to develop an erosion model for ice crystal impingement based on these two phenomena, and to show its capability to predict accretion shape by simulating experimental cases from the National Research Council of Canada (NRC). NRC’s Currie et al. ice crystal experiments [<span class="xref">7</span>] [<span class="xref">8</span>] realized in warm aerodynamic conditions, such as the one encountered in high icing severity areas of a turbofan engine, show accretion severity for a large range of liquid water content to total water content. In order to validate the erosion model based on solid/solid collision, this paper presents the simulation of the lower melting rate experiment. Results show fair agreement with experimental data and allow us to propose pertinent further work.</div></div>

Necessity of multidimensional evaluation of the high-speed ball-end milled surface of hardened AISI D2 steel from a wear resistance perspective

This paper focuses on revealing the anisotropy of surface integrity and wear resistance of high-speed ball-end milled surfaces of hardened cold work die steel AISI D2. Dry milling tests were performed on a five-axis high-speed machining center by using a two-edged coated solid carbide ball-end milling cutter. Then, wear resistance of a hard milled surface was evaluated through block-on-ring wear tests under unlubricated condition. Results showed that ball-end milled surfaces present anisotropic characteristics in terms of surface topography, subsurface microhardness, and yield strength. Moreover, the wear resistance for ball-end milled surfaces shows dependence on sliding direction because of the anisotropy of surface integrity. Benefiting from surface work hardening, wear loss for the hard milled surface was at least 62% less than that for polished ones in the initial wear stage (10 min). However, the subsurface softening zone induced by a high-speed hard milling process has poor wear resistance due to the decrease of microhardness and yield strength. This study indicates the necessity of multidimensional evaluation for high-speed ball-end milled surfaces and the possibility of improving wear behavior by selecting appropriate sliding direction.

Comprehensive modelling, analysis and optimization of furan resin-based moulding sand system with sawdust as an additive

Scarcity of high-cost silica sand, casting defect such as hot tear in hard moulds and casting ejection problem after solidification are the key industrial problems. Sawdust is a by-product of wood working industries, and economic disposal of sawdust in these industries is a growing concern to the wood industries. The present work utilized sawdust as an additive in preparing mould cavity for casting applications. Sand mould properties such as compression strength (CS), mould hardness (MH), gas evolution (GE), permeability (P) and collapsibility (CP) will have good impact on the quality of castings. The effect of variables, namely quantity of resin, hardener, sawdust and setting time, on no-bake furan-bonded sand system is studied in the present research work. The experiments are conducted as per design of experiments, and the data are used to investigate the effect of individual and combined parametric contributions towards responses and establish nonlinear input–output relationships. All nonlinear regression models (that is, input–output relationships) are found to be statistically adequate. The input–output relations are analysed and presented for each of the response with the help of surface plots. Further, the models are found to predict the output close to the experiment (target value). The grand average value in predicting responses is found to be equal to 5.03%. The multi-objective optimization of responses with conflicting nature (minimize: GE and CP; maximize: CS, P and MH) is carried out with the help of global fitness function values determined using genetic algorithm, particle swarm optimization, teacher–learner-based optimization and JAYA algorithms. The optimized values of process parameters that resulted in best set of responses are found to be equal to 60 min, 2.01%, 0.6% and 0.93% for setting time, quantity of resin, hardener and sawdust, respectively. Two automobile coupling parts are cast by pouring molten aluminium into the mould cavity with the optimized and non-optimum sand mould conditions. Further, these two cast components are tested for their quality characteristics, such as surface finish, yield strength, hardness, density and secondary dendrite arm spacing. It has been observed that the quality characteristics of castings produced in mould with optimized parameters are found to be much better.

Surface mechanical properties of shot-peened CNT/Al–Mg–Si alloy composites

A carbon nanotube (CNT)-reinforced Al matrix composite was fabricated and treated by shot peening. After shot peening, isotropic compressive residual stress fields were induced in surface shot-peened layers. As the mechanical properties of the peened layers were improved and therefore varied from the base metal, a specific in-situ X-ray stress analyzer combined with the tensile test technique was used to measure the stress–strain relationship of the strengthened surface layer. On the basis of the measurement and the Von Mises stress criterion, the surface yield strength was calculated and improved by 25% relative to that of the matrix. Moreover, a relaxation behavior of compressive residual stress was observed under cyclic loading. The results showed that the rapid relaxation of surface residual stress chiefly occurred in the first few cycles and then stabilized gradually in subsequent cycles. The retained residual stress under all given applied cyclic loadings possibly occurred in the compressive state consistently.

Finite element analysis of the wear fatigue of rails with gradient structures

We performed the finite element modeling for the first time to analyze the effect of gradient structures (GS) on the wear fatigue-resistant of rails in the rolling-sliding contacts. We found that GS can enhance the wear fatigue-resistant of rails by reducing the maximum horizontal and vertical displacements on the surface of rails. The thicker GS layers, the better the performance is. For a fixed GS layer thickness, increasing the surface yield strength can effectively reduce surface displacements. The outcome from this study can provide the design guideline for processing the gradient structures in the rail steels to obtain superior mechanical properties.

Contact stresses in a fixed-bearing total ankle replacement: A finite element analysis

We performed the finite element modeling for the first time to analyze the effect of gradient structures (GS) on the wear fatigue-resistant of rails in the rolling-sliding contacts. We found that GS can enhance the wear fatigue-resistant of rails by reducing the maximum horizontal and vertical displacements on the surface of rails. The thicker GS layers, the better the performance is. For a fixed GS layer thickness, increasing the surface yield strength can effectively reduce surface displacements. The outcome from this study can provide the design guideline for processing the gradient structures in the rail steels to obtain superior mechanical properties.

Investigation of fatigue performance improvement in SiCw/Al composites with different modified shot peening treatments by considering surface mechanical properties

In order to investigate the fatigue performance improvement of SiCw/Al composite under different shot peening (SP) treatments, conventional SP, warm peening (WP), stress peening (STP) and compound peening (CP) were carried out on SiCw/Al composite specimens. The fatigue test, residual stress measurement and full width at half maximum (FWHM) from X-ray diffraction measurement were conducted on different SP specimens. The fatigue strength of SiCw/Al composite specimen increases by 16%, 37%, 21% and 42% via SP, WP, STP and CP respectively. The surface mechanical properties such as quasi-static surface compressive yield strength (Re(c),s) and cyclic surface yield strength (Rcycle,s) were calculated via analyzing residual stress relaxation during cyclic loading. The results show that the decrement of Re(c),s and Rcycle,s caused by Bauschinger effect during shots' impact is compensated by dynamic strain aging effects in WP and CP. The degree of fatigue strength improvement is more obviously in WP and CP specimens, which is due to the improvement of stability of residual stresses caused by the dynamic strain aging effects in elevated temperature condition.

The modified surface properties and fatigue life of Incoloy A286 face-milled at different cutting parameters

Incoloy A286 alloy is an iron-base superalloy that widely used in gas turbine jet engines and other similar applications, and the high reliability demand of such applications drew significant attention to the machining induced surface integrity and fatigue life. In this work, the Incoloy A286 was face-milled at different cutting parameters, and the surface properties and fatigue life of the modified surface were measured and analysed. It is found that the cutting parameters can modify the surface integrity and mechanical properties significantly, and further obviously influence the fatigue life of the workpiece. The modified fatigue life under different cutting parameters was mainly determined by the roughness and mechanical properties, including the yield strength and fracture toughness, rather than the residual stresses, because of the severe stress relaxation. The surface yield strength had strong positive correlation with the work hardening, while the surface fracture toughness (KJC) was related to the work hardening formation mechanism and grain refinement. The optimal cutting parameters were recommended according to the surface integrity and fatigue life measurement results at last.