喷丸处理对GH3535合金900℃恒温氧化行为的影响

采用不连续增重法,对喷丸状态与非喷丸状态GH3535合金900℃恒温氧化行为进行了对比研究。结果表明,900℃下,喷丸强度0.45Nmm样品与未喷丸样品相比,氧化增重降低了79.7%。未喷丸GH3535合金表面氧化产物为NiCr2O4，MoO2，NiMoO4，喷丸状态下氧化膜主要由NiO、NiFe2O4、Cr2O3和NiCr2O4组成。喷丸处理后GH3535合金表面产生塑性变形使晶粒细化,位错密度增加,在合金表层塑性变形区域的位错及晶界充当了Cr原子的快速扩散路径,增加了Cr原子扩散通量,促进Cr向表面扩散形成富Cr氧化物,使得Cr2O3层的更快形成,减少了瞬态氧化期。     

Detecting recrystallization in a single crystal Ni-base alloy using resonant ultrasound spectroscopy

The use of resonant ultrasound spectroscopy (RUS) as a nondestructive evaluation (NDE) technique for Ni-base single crystal superalloys has been investigated. Manufacture of single crystal superalloys can be challenging due to the prevalence of defects induced during single crystal growth or subsequent processing. Common defects involve the presence of misoriented (non-single crystal) material that change the bulk elastic properties and, as a result, are detectable by RUS. To control the extent of misoriented material, recrystallization induced by shot peening the surface of the single crystal has been studied. RUS was then used to determine the presence and depth of misoriented material due to recrystallization. Recrystallization of shot peened cylindrical single crystal specimens occurred to a depth of 80 μm and 178  μm during subsequent heat treatments. Experimental average resonance frequency shifts of 1.835% ±1.704% and 2.380% ±2.910%, respectively, were measured over a frequency range from 20–200 kHz when compared to the baseline shot peened condition. Finite element (FE) models using the ABAQUS Lanczos Eigen frequency solver assessed the influence of recrystallization as a function of depth from the surface and showed good agreement with the measured resonance frequency shifts. For the greatest NDE sensitivity on production-scale turbine blades and other gas turbine components, a coupled RUS measurement and FE modeling approach is essential, and has the potential to improve single crystal processing approaches and manufacturing yields.     

Evaluating surface deformation and near surface strain hardening resulting from shot peening a tempered martensitic steel and application to low cycle fatigue

The plastic deformation resulting from shot peening treatments applied to the ferritic heat resistant steel FV448 has been investigated. Two important effects have been quantified: surface roughness and strain hardening. 2D and 3D tactile and optical techniques for determining surface roughness amplitude parameters have been investigated; it was found that whilst R_a and S_a were consistent, S_z was generally higher than R_z due to the increased probability of finding the worst case surface feature. Three different methods for evaluating the plastic strain profile have been evaluated with a view to establishing the variation in yield strength near the surface of a shot peened component. Microhardness, X-ray diffraction (XRD) line broadening and electron backscatter diffraction (EBSD) local misorientation techniques were applied to both uniaxially deformed calibration samples of known plastic strain and samples shot peened at intensities varying from 4A to 18A to establish the variation in plastic strain and hence the variation in yield strength. The results from the three methods were compared; XRD and EBSD profiles were found to be the most similar with microhardness profiles extending much deeper into the sample. Changes in the measured plastic strain profile after exposure to low cycle fatigue and the correlation of these changes with the cyclic stress–strain behaviour of the material are also discussed with a view to assessing the importance of the dislocation profile in component life assessment procedures.     

Shot boundary detection using Zernike moments in multi-GPU multi-CPU architectures

This paper presents an analysis of a Multi-GPU Multi-CPU environment, along with the different possible hybrid combinations. The analysis has been performed for a shot boundary detection application, based on Zernike moments, although it is general enough to be applied to many different application areas. A deep study of the performance, bottlenecks and design challenges is carried out showing the validity of this approach and achieving very high frame per second rates. In this paper, Zernike calculations are carried out on GPUs, taking advantage of a packing strategy proposed to minimize host-device communication time.     

Finite element analysis of shot-peening effect on fretting fatigue parameters

Shot peening is widely used to improve the fretting fatigue strength of critical surfaces. Fretting fatigue occurs in contacting parts that are subjected to fluctuating loads and sliding movements at the same time. This paper presents a sequential finite element simulation to investigate the shot peening effects on normal stress, shear stress, bulk stress and slip amplitude, which are considered to be the controlling parameters of fretting damage. The results demonstrated that among the modifications related to shot peening, compressive residual stress has a dominant effect on the fretting parameters.     

A simple but effective FE model with plastic shot for evaluation of peening residual stress and its experimental validation

We propose a practical finite element (FE) model for evaluation of peening residual stress. The model aims to produce a solution approaching the endeavored 3D FE solution. We investigate the effect of physical factors including material damping, dynamic friction and strain rate. The kinematical factors including shot diameter and impact velocity are also considered. Integrating those factors and plastic shots, we set up an effective FE model. Based on the arc height and coverage matching with the Almen saturation curve, impact velocity needed for FE analysis is determined. The model is found to provide the solution comparable with the 3D multi-impact FE solution and the experimental XRD result.     

Effect of Varying Carbon Content and Shot Peening upon Fatigue Performance of Prealloyed Sintered Steels

The aim of the work was to find out how the modification of surface treatment and microstructures affect the fatigue characteristics of the considered sintered materials.Two different systems were prepared:as-sintered and shot peened prealloyed sintered(Astaloy CrL based)steels with addition of 0.5%and 0.7%C.Sintering was carried out in laboratory tube furnace in an atmosphere of pure gases 75%N2+25%H2.The sintering temperature was 1180-C and sintering time was 60 min.Heating and cooling rates were 10-C/min...     

A Comparison Study of Wear and Fretting Fatigue Behavior Between Cr-alloyed Layer and Cr-Ti Solid-solution Layer

This work reported a comparison between the wear and fretting fatigue(FF) behaviors of a Cr-alloyed layer and a Cr-Ti solid-solution layer.The hardness and toughness of both layers were evaluated to support this comparison.The results showed that the Cr-alloyed layer had high surface hardness but poor toughness,while the Cr-Ti solid-solution layer had excellent toughness but low hardness.The FF properties of the modified Ti6A14 V alloy depended on the trade-off between two factors:wear resistance and fatigue resistance.Although the Cr-alloyed layer could effectively resist the wear in fretting areas,its poor toughness caused the fatigue resistance to drop sharply and hence led to a premature failure in FF test.Due to the relatively good fatigue resistance,the Cr-Ti solid-solution layer had slightly higher FF life than that of the Cr-alloyed layer;however,its low hardness resulted in severe wear in correspondence with the fretting area and thus a failure to improve the FF properties of Ti6A14 V alloy.When combined with shot peening post-treatment,the FF life of both layers increased by about three times compared to that of the Ti6A14 V alloy.A further study showed that the poor toughness or low hardness still exerted negative influence on combination-treated samples.     

A Numerical Study Comparing The Effect on Residual Stresses of Two Different Types of Projectiles During Shot Peening

Shot peening is a widely used technique to improve fatigue life in metallic alloys. This processing technique introduces a subsurface compressive residual stress field through a plastic deformation of the surface caused by the impact of a large number of high-speed projectiles. There are a number of parameters that affect the residual stress field depth and magnitude. The effects of the impact angle, shot speed and shot geometry are currently being researched. In particular, substituting spherical cast shots by cylindrical cut wire shots is an attractive option, especially in terms of cost. The effect of shot geometry on residual stresses, however, needs to be further investigated. Because industrial-scale experimentation is costly and cumbersome, mathematical modeling offers a convenient alternative to carry out this type of research. The present work shows a comparison between the residual stresses generated by the impact of spherical and cylindrical projectiles on a steel substrate. This threedimensional model was developed using ABAQUS finite element commercial software (Release 6.12, Dassault Systémes, France). The results show that cylindrical shots generate residual stress fields that are higher in magnitude than those generated by a spherical shot. However, the residual stress field of cylindrical shots impacting the surface at an oblique angle shows an important degree of asymmetry. This effect is not found when spherical shots impact the surface at the same oblique angle.