Work Hardening Effect Research Articles

Plasticizing and work hardening in phase separated Cu-Zr-Al-Nb bulk metallic glasses by deformation induced nanocrystallization

In this work, we report a class of phase separated Cu94−xZrxAl5.5Nb0.5 (x=41, 44, 47, 50at.%) bulk metallic glasses (BMGs) with extraordinary plastic strain up to 43% and work hardening effect featured in the compression strength compared with the yielding strength. Through the characterization of the microstructure, compositional distribution, free volume and activation energy of crystallization, the underlying mechanism for the plasticizing and work hardening has been investigated. It is confirmed that the structural heterogeneity due to the phase separation results in the formation of high density of free volume and low activation energy for crystallization. The deformation induced nanocrystallization (DINC) takes place in the whole region, especially in shear bands (SBs). The DINC may reduce the instabilization of SBs, resulting in the slow-down of the propagation of SBs and the initiation of more primary and secondary SBs from soft to hard region. This may be considered as the underlying mechanism for the plasticizing and work hardening of these BMGs.

Mechanical Characterization of Deformed and Heat Treated Copper-Eutectoid Steel Powder Reinforced Composites

Copper is well known for its formability, conductivity and corrosion resistance properties. The property of pure copper cannot be altered. There is provision in metal family to alter its property by alloying or subjecting to intentional cold deformation. The reinforcement addition introduces miss fit strain in the copper matrix due to the difference in the coefficient of thermal expansion of matrix and reinforcement, the property of copper as a whole is altered. The reinforcement phase alteration by heat treatment changes the room temperature structure of reinforcement, the expansion or contraction of the reinforcement takes place in the matrix, according to the packing efficiency of the room temperature structures formed by heat treatment. Since reinforcement addition may not affect unit cell property of copper, an attempt is made here to reinforce heat treatable ferrous material into the copper matrix. To study the work hardening effect on copper and its composites, cold rolling is also performed to see the extent of property enhancement (hardness). To analyze the dispersion of reinforcements in the matrix, the behavior of reinforcements during tensile fracture and the effect of deformation & rate of cooling on the grain, metallography is also employed. It is expected to improve the hardness and tensile strength of copper considerably with the small addition of reinforcements. Work hardening effect of copper may be enhanced by introducing reinforcements with and without heat treatment, so that the specific weight of copper is substantially improved

The effect of cutting parameters on cutting force and tool wear in machining Nickel Titanium Shape Memory Alloy ASTM F2063 under Minimum Quantity Nanolubricant

The nickel-titanium (NiTi) shape memory alloys have drawn substantial interest among research communities and industries due to their superior properties in shape memory effect and super-elasticity as compared to the typical alloys and super-alloys. The use of this material in biomedical applications has now been widely recognized and accepted due to its biocompatibility to human body. For instance, NiTi alloys under the ASTM F2063 classification are often applied in medical devices and surgical implant applications. However, due to their poor thermal conductivity and high strain or work hardening effects, a number of complications arise when secondary manufacturing processes such as machining are carried out on these alloys. The use of appropriate coolant technology should be able to overcome these problems through effective cooling and lubricating near the cutting zone. In the present study, the influences of machining parameters, namely; cutting speed, feed rate and depth of cut, on the cutting forces and tool wear have been investigated under two modes of cutting environment, namely, dry and minimum quantity nanolubricants. The results show that minimum quantity nanolubrication with aluminium oxide nanoparticles leads to a notable effect in alleviating the amount of tool wear and at the same time controlling the development of cutting force. The reduction in the cutting force and tool wear while applying the minimum quantity nanolubricants is approximately 6-10% and 4-30%, respectively; as to that of dry cutting. It was also observed that the main mechanisms of wear for all conditions are mainly abrasion on the flank face of the cutting inserts. As a whole, the lubrication approach suggested in this study is an effective strategy to reduce ecological impacts and offer cost effective alternative for machining these unique alloys.

Study of PSHG and its integrated hardening model of hardening layer

Pre-stressed hardening grinding (PSHG) combines with the advantage of grinding hardening and pre-stressed grinding. Ideal residual stress can be obtained along with the hardening effect on the surface of workpiece. In order to study its unique hardening characteristic, the paper divided the comprehensive hardening effect of PSHG into quench-hardening effect and work-hardening effect. Combining with the PSHG experiment, the quench hardening rules and mechanism were studied. The stabilization of parent phase and dislocation-induced nucleation due to applying pre-stress has comprehensive effect on the martensite transformation. So, the quench-hardening effect increases first and then decreases with the increasing of pre-stress. From the perspective of energy transformation, a model of quench hardening was established which can describe its relation with pre-stress in PSHG. The mechanism of the work hardening was analyzed. And a simulation model was established using ANSYS which can describe the relation between work-hardening effect and the pre-stress. It reveals the pre-stress restrains the work-hardening effect due to its influence on dislocation of surface materials, especially when the depth of cut is small.

Crack driving forces for short cracks: The effect of work hardening

The effect of hardening on the crack tip deformation of short cracks is investigated by FEM analysis. The analyses of the results show that the commonly used Shih-Hutchinson and Dowling equations for the calculation of the J integral are very good approximations for small and large scale yielding conditions. This method is developed for hardening materials and provides a rough approximation for ideal-plastic or even for softening materials, as long as full scale yielding does not take place. However, in the case of full scale yielding these equations do not provide a satisfying estimation of the J integral or crack tip deformation for non-hardening or softening materials, due to a strong dependency on the plastic correction factor. The impact of this phenomenon for nanocrystalline metals or metallic glasses will be pointed out shortly.

The effect of work-hardening and thermal annealing on the early stages of the uranium-hydrogen corrosion reaction

The characteristics of hydride formation on metallic U at the early stages were investigated for three differently treated samples. The first sample reacted in its as-received state, the second was thermally annealed and the third sample underwent cold work-hardening prior to reaction with deuterium. From the analysis, the vacuum heat-treated sample was found to be more resilient to hydriding at the nucleation and growth stage, exhibiting a reduced number of nucleation points when compared to the as-cast uranium. The work-hardened sample was observed to be more susceptible to H2 corrosion, displaying very dissimilar hydriding behaviour when compared to the other.

Microstructural evolution and constitutive analysis combined with weight optimization method of Al-7.82Zn-1.96Mg-2.35Cu-0.11Zr alloy during hot deformation

Isothermal hot compression tests of Al-7.82Zn-1.96Mg-2.35Cu-0.11Zr alloy were carried out on a Gleeble-3500 thermo-simulator in the temperature range of 573–733 K and strain rate range of 0.001–1 s−1. Stress-strain curves show that work hardening effect progressively exceeds softening effect with increasing strain rate. Microstructural evolution shows that two kinds of dynamic recrystallization exist in the hot compression process, which includes continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) and the dominant mechanism is continuous dynamic recrystallization, which occurs under the combined action of progressive subgrain rotation and misorientation increase. Five constitutive models were constructed to describe the hot deformation behavior. Weight optimization model has lower average absolute relative errors (AARE) value of 2.78%, root mean square error (RMSE) value of 2.73 and higher correlation coefficient (R) value of 0.997, and gives weight factors at different temperatures. The revised constitutive model with considering the comprehensive effects of lattice diffusion, grain boundary diffusion and the results of weight optimization gives relatively high prediction precision with AARE value of 4.64%, RMSE value of 4.92 and R value of 0.995, which is second to that of weight optimization model. The main diffusion mechanism is dominated by grain boundary diffusion at 573–693 K and lattice diffusion at 733 K.

Effects of laser shock peening with contacting foil on micro laser texturing surface of Ti6Al4V

Ti6Al4V samples with micro-dimple arrays were subjected to laser shock peening in contact with foil (HCLSP). The surface roughness, micro-hardness, the residual stress distribution and the surface morphology of the micro-dimple arrays were studied to evaluate the effects of HCLSP. Moreover, the surface topography of the foils in contact was also analyzed. The gap existence between the foil and the to-be treated surface led the mechanism of HCLSP to be different compared to regular laser shock peening. The surface roughness reduction, the work-hardening effects, the compressive residual stress and the micro crack enclosure were achieved. A simplified ball-hitting-surface model was utilized to analyze the HCLSP impact. The model could well explain the experimental results. When treated by the HCLSP with H62 foil at the laser power density of 4.24 GW/cm2, the Ti6Al4V samples with micro-dimple arrays exhibit well surface topography and mechanical performance.

Low-Velocity Impact Wear Behavior of Ball-to-Flat Contact Under Constant Kinetic Energy

The impact tests were conducted on metallic materials with different bulk hardness and Young’s moduli. Analysis of the dynamics response during the tribological process showed that the tested materials had similar energy absorption, where the peak contact force increased as the tests continued. Moreover, wear volume decreased with the increase in Young’s modulus of metals, except for Cr with a relatively low hardness. Wear rate was gradually reduced to a steady stage with increasing cycles, which was attributed to the decrease in contact stress and work-hardening effect. The main wear mechanism of impact was characterized by delamination, and the specific surface degradation mechanisms were depending on the mechanical properties of materials. The absorbed energy was used to the propagation of micro-cracks in the subsurface instead of plastic deformation, when resistance of friction wear and plastic behavior was improved. Hence, both the hardness and Young’s modulus played important roles in the impact wear of metallic materials.

Effects of punching process on crystal orientations, magnetic and mechanical properties in non-oriented silicon steel

In an attempt to investigate the effects of punching process on crystal orientations, magnetic and mechanical properties in non-oriented silicon steel, the steel sheet was punched for circular shape of Φ40mm. The crystal orientations and small-angle grain boundaries were characterized by electron backscatter diffraction (EBSD). The results indicated that the initial crystal orientations within a distance of 200μm away from the sheared edge were significantly changed after the punching process. In this area, the fractions of the directions with a high value of magnetocrystalline anisotropy energy Ea, 〈111〉, 〈212〉 and 〈112〉 can reach up to 0.619. However, the fractions of the directions 〈001〉 and 〈113〉 accounts for only 0.096, which have a lower value of Ea. Moreover, the fraction of small-angle grain boundaries markedly increased in the area of about 200μm from the sheared edge, which is mainly attributed to the dislocations multiplication and dislocations motion. The magnetic domain structures were characterized by an optical microscope according to the Bitter method. The results showed that the width of magnetic domain in the sheared edge was much larger than that in the center and the patterns also existed a big difference. The Vickers HV0.1 method was employed to measure the microhardness of the sheared edge. It was found that the values of microhardness within a distance of 400μm away from the sheared edge decreased from 259 to 167 due to the effect of work hardening, which is mainly caused by the dislocations pile-ups near the grain boundaries.

Scope for improved properties of dissimilar joints of ferrous and non-ferrous metals

Dissimilar joints (DSJs) of ferrous and non-ferrous metals have huge technological importance in the frontiers of new designs in new machineries and improved design of conventional systems. This investigation was undertaken to improve mechanical properties of joints of two dissimilar metals: one is Ti-based and the other is Fe-based. DSJs were processed using bonding pressure from 1 to 9 MPa in step of 2 MPa at 750 °C for 60 min. Properties of the DSJs of these two metals using different mechanisms and methods were compared with the present research for verification. Experimental results from the diffusion bonding mechanism for joining the dissimilar metals validated the improvement in properties. Superior mechanical properties of dissimilar-metals joints were achieved mainly due to the third non-ferrous metallic foil, Ni of ~ 200-μm thickness, which avoided the formation of brittle Fe–Ti-based intermetallics in the diffusion zone. DSJs processed are able to achieve maximum strength of ~560 MPa along with substantial ductility of ~11.9%, which is the best ever reported in the literatures so far. Work hardening effect was detected in the DSJs when the bonding was processed at 5 MPa and above. Bulging ratio of the non-ferrous metal (Ti-based) was much higher than that of the ferrous metal (SS) of the DSJs processed. SEM analysis was carried out to know the details of reaction zone, while XRD was carried out to support the SEM results. Reasons for change in mechanical, physical, and fracture properties of the DSJs with the process parameter variations were clarified.

Effect of ultrasonic impact treatment on the ultra high cycle fatigue properties of SMA490BW steel welded joints

Effect of ultrasonic impact treatment on ultra high cycle fatigue properties of SMA490BW steel welded joints was studied from the aspects of stress concentration of weld toe, residual stress distribution, and surface grain size. The results show that the ultrasonic impact treatment can significantly improve the high cycle and very high cycle fatigue strength of welded joints. After treated by ultrasonic impact, the stress concentration factor of weld toe is decreased by 19.1%. And residual tensile stress of weld toe is eliminated, which change into the beneficial residual compressive stress. Residual compressive stress increases the fatigue crack propagation threshold, inhibiting the expansion of early fatigue crack, so as to effectively prolong the fatigue life of welded joints. The surface grains of weld toe can be refined by ultrasonic impact treatment, and nanocrystalline structure with random orientation distribution can be obtained. Grain refinement and work-hardening effects cause the increase of microhardness on surface.

High‐Temperature United Constitutive Model of Non‐Oriented Electrical Steel Based on Transformation Kinetics Equation and Dislocation Density Theory

The deformation resistance of non‐oriented electrical steel not only depends on the deformation temperature, strain, and strain rate, but also closely relates to the phase transformation. This study aims to incorporate these effects into a united constitutive model and make clear the distinction of micro hardening and softening mechanisms in different phase regions. Firstly, the transformation kinetics equation is established by the thermal dilatometric tests to accurately quantify the transformation process. Then, the high‐temperature deformation constitutive models are developed for each phase region based on the hot compression experiments and the dislocation density theory. The Hardening‐Softening Ratio is also proposed to describe the combined effect of work hardening and dynamic recovery softening. Finally, the model predictions are compared to the measured data and show a good fit. The results show that yield stress has a negative tendency with temperature in the ferrite region and also in the austenite region, and it changes faster in the ferrite region. The material constant is mainly related to the phase structure but almost independent of temperature. The hardening coefficient is determined by both temperature and phase structure, and the softening coefficient mainly depends on the phase structure.

Evolution of stacking fault tetrahedral and work hardening effect in copper single crystals

Stacking fault tetrahedral (SFT), generated in machining of copper single crystal as one type of subsurface defects, has significant influence on the performance of workpiece. In this study, molecular dynamics (MD) simulation is used to investigate the evolution of stacking fault tetrahedral in nano-cutting of copper single crystal. The result shows that SFT is nucleated at the intersection of differently oriented stacking fault (SF) planes and SFT evolves from the preform only containing incomplete surfaces into a solid defect. The evolution of SFT contains several stress fluctuations until the complete formation. Nano-indentation simulation is then employed on the machined workpiece from nano-cutting, through which the interaction between SFT and later-formed dislocations in subsurface is studied. In the meanwhile, force-depth curves obtained from nano-indentation on pristine and machined workpieces are compared to analyze the mechanical properties. By simulation of nano-cutting and nano-indentation, it is verified that SFT is a reason of the work hardening effect.

Constitutive model and optimal processing parameters of TC17 alloy with a transformed microstructure via kinetic analysis and processing maps

The kinetic and flow stability analysis of TC17 alloy with a transformed microstructure in the hot deformation of α+β region were carried out. The flow behavior in the hot deformation of TC17 alloy was sensitive to the strain, strain rate and deformation temperature. The work hardening effect dominated the flow in the early stage of deformation, and the globularization, dynamic recrystallization (DRX) occurred in the following deformation, in which the apparent activation energy for deformation decreased with the increasing of strain. A strain compensated constitutive model for hot deformation of TC17 alloy was established. The peak efficiency of power dissipation at the strains of 0.3 and 0.5 occurred at 0.01s−1 and 1143K due to α to β transformation and DRX of β phase. However, the peak efficiency of power dissipation at a strain of 0.7 occurred at 0.1s−1 and 1123K due to the globularization of α lamellae and DRX of β phase. The flow instability analysis suggested that the safe processing window should not exceed 0.32s−1. The processing maps of TC17 alloy at different strains were constructed. According to the processing maps and microstructure observation, the optimal processing parameters for globularization of TC17 alloy with a transformed microstructure were at the temperatures ranging from 1043K to 1123K and strain rates ranging from 0.01s−1 to 0.1s−1.

Reverse deep drawing process: Material anisotropy and work-hardening effects

The present work aims to study the constitutive models’ influence on the reverse deep drawing simulation of cylindrical cups. Several constitutive laws were considered to predict the combined effects of anisotropy as well as the changes in strain path direction of the stainless steel. To this end, a number of models were used, worth mentioning among which are the isotropic with nonlinear kinematic hardening laws, along with the isotropic von Mises and anisotropic Hill’48 yield criteria. For the models’ parameters identification, uniaxial tensile and shear tests at several orientations to the rolling direction as well as reversed shear tests were carried out. Then, a subsequent comparison between experimental data and numerical simulations of reverse deep drawing tests were performed, using the finite element code Abaqus/Explicit. On the basis of the major reached results, it has been found that for the first stage, whatever the yield criteria used and for all the hardening models, the numerical punch-force evolution correlates well with the experimental one. For the second stage, the punch-force evolution was found to be remarkably more influenced by the yield criteria than by the kinematic laws. The major strain distribution greatly depends on the yield criteria. Meanwhile, it was slightly linked to the work hardening.

The effect of in-service work hardening and crystallographic orientation on the micro-scratch wear of Hadfield steel

This work presents the micro-scratch wear analysis of a sample of Hadfield steel previously used in a jaw crusher machine. The in-service work hardening material derived from dynamic high loads during the abrasive contact on the steel surface. The scratch resistance of hardened samples was evaluated by micro-scratch tests on a cross-section surface. Scratches were made on a deformed layer and on an undeformed material. In the undeformed region, the two crystallographic planes 001 and 111 were analyzed. The scratch tests were performed under various normal loads (from 20 mN to 250 mN) with a diamond cone stylus of 60° and a 5 μm radius. The electron microscopy techniques (FEG, FIB, and EBSD) were applied to characterize the microstructure, the wear micromechanisms, and the change of the submicrostructure due to scratches and crystallography. Additionally, an optical interferometry analysis was done for the topography characterization of the scratches. The microhardness profile analysis showed a variation of the hardness values from 300 to 700 HV0.3, which resulted from the twinned grains found near the worn surface. Low loads (20 mN and 50 mN) corresponded to mild wear regime, with a wear regime transition at 100 mN. A severe wear regime corresponded to higher loads (150 mN, 200 mN, and 250 mN). A significant variation of the friction coefficient along with the severely hardened layer for low normal loads was not observed. On the other hand, high loads resulted in significant variations of the friction coefficient, without correlation with microhardness profile. Additionally a strong relationship was observed between the scratch wear and the individual grain crystallographic orientation. For scratches in the (001) plane microploughing was established as the predominant wear micromechanism, whereas for (111) plane microcutting was identified as the micromechanism responsible for wear, presenting a higher friction coefficient than for the (001) plane.

Evaluation of deformation stability and fracture mechanism in incremental sheet forming

Incremental sheet forming (ISF) is a flexible process for rapid manufacturing of complex sheet metal parts. An advantage of ISF is the improved formability than traditional sheet forming processes such as stamping. A number of fundamental studies have been conducted to investigate the enhanced ISF formability considering the effects such as bending under tension and through thickness shear. To further understand the ISF deformation mechanism and formability enhancement, this work presents a new analytical model which is focused on investigating the deformation stability and its effect on the metal sheet fracture. Based on this new model, the critical strain of deformation instability is obtained. Furthermore, influences of the work-hardening effect and bending effect on the deformation stability are investigated. To validate the analytical model, the fracture occurrence of two aluminum grades, AA1100 and AA5052, are investigated by using ISF experiment. Based on the analytical and experimental investigation, this study has concluded that bending plays a major role on ISF deformation stability. In addition, the ISF fracture depends on both deformation stability and the sheet material's ductility.

Multi-stage cold forging process for H68 brass cylindrical shell part with deep blind hole: simulation and experiment

The classical manufacture technology of H68 brass cylindrical shell part with deep blind hole is machining process, which can achieve requirements of dimension precision, but the process has lower efficiency, and the strength and toughness of the parts do not satisfy the usage requirements in the industry. The multi-stage cold forging process, which could improve the mechanical properties of the parts, is used to replace the traditional machining process. The process designs of multi-stage cold forging process for parts have been studied, including several operations such as annealing, initial upsetting, preforming, back extrusion, ironing, and upsetting flange. In order to ensure the multi-stage cold forging process, one finite element (FE) simulation, used to study strain distributions and flow lines, is conducted. Based on the FE results, several cold forging dies have been designed and manufactured. The experimental work shows that the cold work-hardening effect is obtained, and distribution of flow lines is reasonable; precision accuracy and mechanical properties meet the technical requirements, and production efficiency has been improved significantly.

Influence of Shot Peening on DIN 1.2714 Hot Work Tool Steel

Shot peening is one of the most popular surface enhancement technique used to improve fatigue performance of different materials. This paper focuses on to study the effect of different shot peening parameters on micro-structural and mechanical properties of DIN 1.2714 tool steel specimens. Shot peening treatments were carried out by varying shot size and peening intensity. X-ray stress analysis, micro-hardness testing and micro-structural analysis were performed to characterize these specimens. In addition, pin on disk wear testing was executed to recognize wear behavior of this shot peened tool steels. It was observed that along with compressive residual stress generation, shot peening also induces work hardening effect and modifies surface structure which are responsible for significant improvement in this tool steel.