Subsurface Plastic Deformation Research Articles

An analytical model for predicting the depth of subsurface plastic deformation during cutting titanium alloy

An analytical model for predicting the depth of subsurface plastic deformation during cutting titanium alloy

Study on the subsurface characteristics of textured surfaces under EHL condition

PurposeThe purpose of this study is to investigate the influence of surface texture on the subsurface characteristics of contact interfaces under elastohydrodynamic lubrication condition. As a typical contact form of gears and bearings, the optimization of friction characteristics at the elastohydrodynamic lubrication (EHL) interface has attracted the attention of scholars. Laser surface texturing is a feasible optimization solution, but there have been concerns about whether the surface texture of high-pair parts will affect their fatigue life.Design/methodology/approachTo examine the impact of texture preparation on the subsurface characteristics of high-pair interfaces under EHL conditions, a point contact EHL model is developed that takes into account the effect of textured surface topography. The pressure and thickness of the oil film are calculated as input parameters under different loads and entrainment velocities. The finite element method is used to simulate the impact of textures with varying diameters, densities and depths on the subsurface characteristics of the elastohydrodynamic interface. According to ISO 25178, analyze the relationship between 3D topography parameters and subsurface characteristics and study the trend of friction characteristics and subsurface characteristics based on the results of the ball on disc friction tests.FindingsThe outcomes suggest that under different rotational velocity and load conditions, the textured surfaces exhibit improved friction reduction effects; however, the creation of textures can result in significant subsurface plastic deformation and local peeling. The existence of texture makes the larger stress zone in the subsurface layer closer to the surface, leading to fatigue failure near the surface. Reasonable design parameters can help enhance the attributes of the subsurface. A smaller Sa and a Str greater than 0.5 can achieve ideal subsurface properties on the textured surface.Originality/valueThis paper investigates the influence of surface texture on the friction and subsurface characteristics of EHL interfaces and analyzes the impact of surface texture on interface contact performance while achieving lubrication improvement functional characteristics. The results provide theoretical support for the optimization design and functional regulation of surface texture in EHL interfaces.Peer reviewThe peer review history for this article is https://publons.com/publon/10.1108/ILT-10-2023-0324/

Enhanced scale inhibition and anti-wax capacities of passive materials via ultrasonic rolling processing

Scale damage and wax formation on pipelines surface have become prevalent issues in the development and production of the oil and gas industry throughout the world. The utilization of the ultrasonic surface rolling process (USRP) on pipeline surfaces is a promising protective approach and its universal verification for the enhancement of the scale inhibition and anti-wax capacities of passive materials is presented in this work. The effect of USRP on surface integrity (including roughness, cross-sectional microstructure, residual stress and water contact angle), scaling and wax deposition behavior, passive film structure and characteristics are experimentally analyzed by comparing three passive materials (13Cr stainless steel, 825 nickel-base alloy and Ti6Al4V alloy) with 3Cr carbon steel. The results indicate that USRP can effectively reduce the surface roughness and contribute to the growth of passive film due to the enriched passive elements on the metal surface, which consequently endow the passive materials with reduced surface free energy and enhanced anti-scaling/anti-wax capacities. Furthermore, benefitting from the surface passivation, the enhancement in the corrosion resistance of the film helps to provide good chemical stability. The main reason for why USRP has a protective effect on the scale inhibition and anti-wax capacities of the passive materials is also elucidated. The input energy of USRP not only achieves chip-free polishing and triggers structural response changes in the surface and subsurface plastic deformation but also produces a unique passivation response that can alter the chemical composition, thickness, compactness and defect density of the passive film. This in turn leads to significant changes in its corrosion resistance, which is related to the semiconductor characteristics of the materials, surface energy, and hydrophilic–hydrophobic physical and chemical properties. This results in a significant inhibitory effect on the deposition of scaling ions or wax crystals at the passive film/solution interface.

A Finite Element Assessment of The Workpiece Plastic Deformation in Machining of Ti-6Al-4V

Severe plastic deformation is not desired in machining as it adversely affects surface integrity. In this study, the performance of finite element formulations on subsurface plastic deformation is studied. Finite element models of orthogonal milling of Ti6Al4V have been developed using Update Lagrangian with element deletion as well as continuous remeshing algorithms. The models are validated not only by the measured cutting forces, but quantitative measurements of the subsurface plastic deformation. The results showed that continuous remeshing strategy generate smooth milling forces and predicted the plastic deformation of the machined subsurface with higher accuracy compared to the element deletion method.

Microstructure and surface integrity of machined AZ91 magnesium alloy

AZ91 magnesium alloy is one of the most popular materials among all cast magnesium alloys due to its excellent corrosion resistance and good cast-ability. Although AZ91 is categorized as soft materials and easy-to-cut, there are many challenges in the finish machining of AZ91. In this research, a comprehensive as well as novel study on the surface integrity of machined AZ91 magnesium alloy is presented. To this end, AZ91 samples are machined under different cutting conditions and afterward, both surface and subsurface features are analyzed. Assessing the finished surface is conducted by surface 3D topography, roughness measurement, and scanning electron microscope. In terms of subsurface characterization, the effect of machining conditions cutting speed and feed rate on the micro hardness variation, subsurface microstructure changes, plastic deformations, and subsurface defects are studied. Results indicated that when machining AZ91, surface defects mostly are formed around the secondary phases. Moreover, twining and shear bands are the main microstructural changes close to the machined surface. Additionally, finishing machining of AZ91 induced subsurface plastic deformation to the depth of 180 μm as well as micro cracks propagation, in secondary phases, to nearly 100 μm under the machined surface.

Effects of Cutting Edge Radius on Surface Integrity in Machining of Nickel-Based Cast Superalloy: An In Situ Imaging Approach

Abstract Cutting edge radius is a crucial factor affecting surface integrity during metal machining, which determines product performance. However, the exact mechanism of how the cutting edge radius affects machined surface has not yet been understood, especially lacking in situ evidence during the material removal process. In this article, effects of cutting edge radius on surface roughness, subsurface deformation, and work hardening of nickel-based cast superalloy are studied through an in situ imaging approach. Based on continuous high-speed filming and digital imaging correlation (DIC) techniques, detailed chip formation and quantitative subsurface plastic deformation under various cutting edge radii are analyzed, and the formation of built-up edge (BUE) is observed when using a large edge radius. Furthermore, when the cutting edge radius is greater than the uncut chip thickness (h), the thickness of plastic deformation increases dramatically. On the other hand, the machined surface roughness can be improved when the cutting edge radius is between 30% and 60% of h. The sharp cutting tools or the cutting edge radius higher than 60% of h result in a poor surface quality on the machined surface during nickel-based cast superalloy machining. The effects of cutting edge radius on machined surface generation are systematically categorized as cutting with chipping, cutting with significant plowing, and cutting with plowing accompanied by BUE formation.

Effect of cutting edge radius when milling hardened steels: a finite element analysis and surface integrity investigation

This work investigated the impact of cutting tools varying edge radii by presenting a 3-dimensional finite element analysis (3D FEA) model during the milling of hardened steels. The proposed numerical model was able to capture the effect of micro geometrical changes between cutting tools of five different edge radii (25 30 35 40 and 45 ). Experimental milling tests were performed to validate the numerical model and close agreement was reported between the experimentally acquired cutting forces and the numerically simulated ones. Results concluded that experimental and numerical cutting forces increased with the increase of edge radius. Furthermore, the effect of the five different edge radii and cutting conditions on the integrity of machined surfaces were studied. The integrity parameters of choice were surface roughness, feed marks pattern, subsurface plastic deformation, and subsurface microhardness. Results indicated that the surface roughness increased with increasing the feed rate and decreasing the cutting speed, and vice versa. However, altering the edge radius did not introduce a significant impact on the surface roughness. Results also revealed that increasing the edge radius made feed marks more visible and increased the subsurface plastic deformation and microhardness beneath the machined surface.

Rapid non-destructive sizing of microstructural surface integrity features using x-ray diffraction

In this study, rapid non-destructive sizing of machining-induced subsurface white layers and plastic deformation is achieved through x-ray diffraction peak breadth measurements. Sizing to within 0.5–2 μm is shown to be possible for features thinner than the x-ray penetration depth with inspection times under 1 min achievable. Whilst the technique can detect features larger than the penetration depth, accurate sizing is not possible. Appropriate selection of different x-ray radiation and diffraction peaks can be used to increase or decrease the penetration depth to improve sizing accuracy at larger and thinner feature thicknesses, respectively. However, there is a depth limit for each material imposed by the smallest wavelength of radiation that can be used and the highest angle diffraction peak that can be resolved. The dependence of peak breadth on deformation or white layer thickness can be modelled by assuming a linear or exponential decay in strain across the feature thickness.

Microstructure- and cooling/lubrication environment-dependent machining responses in side milling of direct metal laser-sintered and rolled Ti6Al4V alloys

Ti6Al4V manufactured by direct metal laser sintering (DMLS) is a difficult-to-cut material and has a different microstructure to conventional Ti6Al4V. Therefore, this work aims to investigate the influence of microstructure characteristic and sustainable cooling/lubrication method on machining responses of Ti6Al4V. Side milling tests were performed under dry and supercritical CO2-based minimum quantity lubrication (scCO2-MQL) conditions. Experimental materials were DMLS-produced Ti6Al4V and conventional rolled one. Milling force, subsurface microstructure evolution, crystallographic texture, and residual stress were evaluated. For DMLS Ti6Al4V, subsurface plastic deformation depth increased with increasing cutting speed vc. Only under the most drastic condition (highest vc = 180 m/min, dry milling), a white layer with grain refinement down to 0.4 μm was formed, which resulted from α→β phase transformation and twinning-induced dynamic recrystallization. The activated twinning within the grain refinement layer was 101¯21¯011 and 101¯11¯012 twinning. For conventional Ti6Al4V, in contrast, no subsurface microstructure evolutions were identified after milling. Milled surface of rolled Ti6Al4V exhibited residual tensile stresses while DMLS Ti6Al4V exhibited residual compressive stresses. Milling force of rolled alloy was 15 % higher than DMLS-produced one. The different cutting responses of the two alloys are attributed to the fact that rolled Ti6Al4V has fine-grained microstructures while DMLS alloy has coarse-grained microstructures. The proposed scCO2-MQL method can improve machinability and surface integrity, and suppress the activation of high order twinning of DMLS Ti6Al4V. This study’s findings may be useful in developing finite element or analytical models for predicting the microstructural variations of DMLS Ti6Al4V during cutting.

Machining subsurface deformation under various rake angles

Subsurface plastic deformation has attracted a great deal of attention due to its tight relation with surface hardening, microstructure alteration, grain refinement, and white layer formation. Therefore, it is critical to study the subsurface plastic deformation during the machining process. In this study, the digital image correlation technique (DIC) is used to measure the subsurface deformation during the orthogonal cutting process. The cutting tool’s rake angle is varied by a specially designed experimental setup. FEM simulations are carried out to predict the subsurface deformation and comparisons with the experimental measurements are conducted. This study can deepen the understanding of the generation of surface integrity and can be further developed for implementation into the online conditioning of surface integrity.

A study on strengthening and machining integrated ultrasonic peening drilling of Ti-6Al-4V

In aircraft assembly filed, introducing compressive residual stress by cold expansion around the fastening hole is considered as a common method to enhance hole fatigue resistance. However, the conventional cold expansion technology inevitably extends the processing cycle of fastening hole. Therefore, this study proposes a strengthening and machining integrated ultrasonic peening drilling (UPD) to solve this problem by introducing ultrasonic vibration perpendicular to the hole surface during drilling. Both the strengthening principle and dimension accuracy improvement mechanism in UPD were analyzed to better understand the cutting mechanism. The feasibility experiments of UPD of Ti-6Al-4V were conducted to evaluate surface integrity and machining accuracy. The results show that compared to conventional drilling (CD), smoother machined surface and narrower dimensional tolerance were obtained with UPD. Moreover, the subsurface plastic deformation was increased by as high as 4 times with severer deformation degree. Accordingly, the surface residual stress and the depth of circumferential residual stress in the subsurface was increased by 115.7% and 125% respectively. In addition, surface micro-hardness and subsurface hardening layer depth were also significantly increased. The results demonstrated that UPD achieved the integration of strengthening and precision-machining and could be a promising method for finish drilling of aircraft fastening holes.

Experimental investigation on the effects of machining parameters on surface integrity in form grinding of rail material

Rail grinding is an essential measure for the maintenance of railway infrastructure, and the machined surface integrity of rail material plays a crucial role in ensuring the safety, stability and service performance of the railway network. In this paper, an electroplated diamond grinding wheel was employed to re-profile the rail surface. Meanwhile, single-factor experiments on the form grinding of rail material were designed and carried out by virtue of the self-developed rail grinding platform under dry grinding condition based on proper machining parameters. The effects of machining parameters on the surface roughness, subsurface micro-hardness, plastic deformation, and surface morphology were investigated, respectively. The experimental results revealed that the surface roughness and subsurface micro-hardness increase with the increase of feed speed and grinding depth, while decrease with the increase of wheel peripheral speed. The thickness of subsurface plastic deformation layer and the degree of plastic flow increase with the increase of grinding depth, and the thickness of subsurface plastic deformation layer ranges from 7 μm to 14 μm with the change of grinding depth.

Experimental Investigation on the Wear and Damage Behaviors of Machined Wheel-Rail Materials under Dry Sliding Conditions.

Rail grinding and wheel turning can effectively remove surface defects and unevenness, which is a crucial process for the safe and smooth operation of trains. Machined surface integrity of wheel/rail materials significantly influences their tribological property. In this study, firstly, the rail blocks were ground via a cylindrical grinding machine, and the wheel rings were turned by a computer numerical control (CNC) lathe with varied parameters. Then, the sliding wear and damage characteristics of the machined wheel/rail samples under dry conditions were studied by virtue of a block-on-ring tribometer. The results show that the surface microhardness of the ground rail blocks is larger than that of wheel rings, while the surface roughness and the thickness of the subsurface plastic deformation layer (SPDL) of rail blocks are much smaller than those of wheel rings. After sliding, the surface microhardness of wheel/rail samples increases remarkably. The thickness of the SPDL, the wear loss, and the increase degree of surface microhardness of rail blocks are larger than those of wheel rings. Surface microhardness, roughness and the SPDL of the machined wheel/rail samples impose a combined influence on the anti-wear property, and the tribological pair with proper initial surface roughness and microhardness engenders the smallest amount of total wear loss.

Study on the subsurface damage mechanism of optical quartz glass during single grain scratching

The single grain scratching SPH simulation model was established to study the subsurface damage of optical quartz glass. Based on the analysis of the stress, strain and scratching force during scratching, the generation and propagation of subsurface cracks were studied by combining with the scratch elastic stress field model. The simulation results show that the cracks generate firstly at the elastic-plastic deformation boundary in front of the grain (φ = 28°) due to the influence of the maximum principal tensile stress. During the scratching process, the median crack closes to form the subsurface damage by extending downward, the lateral crack promotes the brittle removal of the material by extending upward to the free surface, and microcracks remain in the elastic-plastic boundary at the bottom of the scratch after scratching. The depth of subsurface crack and plastic deformation increases with rising scratching depth. The increase of scratching speed leads to the greater dynamic fracture toughness, accompanied by a significant decrease of the maximum depth of subsurface crack and the number of subsurface cracks. The subsurface residual stress is concentrated at the bottom of the scratch, and the residual stress on both sides of the scratch surface would generate and propogate the Hertz crack. When the scratching depth is less than 1.5 μm or the scratching speed is greater than 75 m/s, the residual stress value and the depth of residual stress are relatively small. Finally, the scratching experiment was carried out. The simulation analysis is verified to be correct, as the generation and propagation of the cracks in the scratching experiment are consistent with the simulation analysis and the experimental scratching force indicates the same variation tendency with the simulation scratching force. The research results in this paper could help to restrain the subsurface damage in grinding process.

Flooded drilling of Inconel 718 using graphene incorporating cutting fluid

In order to improve drilling performance of Inconel 718 alloy, a cutting fluid (CF) consisting of 70% water and 30% vegetable oil blended with graphene nanoplatelets was used. Sliding of Inconel 718 workpiece using WC-Co drills with CF containing 54 × 10−5 wt% graphene (GCF) reduced the coefficient of friction (COF) between the tool and workpiece surfaces from 0.16 to 0.08 and resulted in the formation of tribolayers. The maximum drilling torque of 6 Nm for CF was reduced to 2 Nm using GCF. Additionally, arithmetic mean height (Sa) of drilled surfaces decreased from 8 to 4 μm and a reduction in the amount of material transferred from the Inconel 718 to the cutting edge of the drill was observed. The drilling temperature decreased from 150 to 100 °C using GCF during the process. Subsurface plastic deformation that occurred at the drilled surfaces of Inconel 718 was examined by cross-sectional optical microscopy which revealed that both the depth of deformation zone and the magnitude of subsurface strains were lower compared with flooded drilling. Therefore, graphene added in small quantities to the cutting fluid can provide an energy efficient method for drilling of Inconel 718. Graphical abstract

Analytical model and experimental verification of Poisson burr formation in ductile metal machining

Previous investigations on the theoretical model to predict burr dimensions have normally been confined to a single geometric model, and the findings that have been proposed rarely take into account the influence of multi-physics factors on burr formation in the complex machining process. This paper proposes an analytical model to reveal subsurface plastic deformation behavior in machining of ductile material. This model is developed based on coupled thermo-mechanical factors. More importantly, the material property and tool edge arc are taken into consideration. According to the proposed model, the two approaches are presented to predict Poisson burr height and root thickness. Moreover, the material flow and burr formation mechanism are further investigated at great length. The effects of machining parameters and material properties on burr formation are analyzed and discussed in terms of plastic deformation behavior. The results show that this proposed model can describe burr morphology and predict burr size accurately. Poisson burr generation has a great sensitivity to machining parameters, as well as material property, and the transition of burr morphology is caused by severe lateral material flow owing to material softening effect at high temperature. There is the synchronous interaction between machining parameters and material property influencing burr formation. As a result, this study provides a valuable theoretical reference and basis for the deburring energy minimization, high surface quality, and machining parameters optimization.

Micromachining imposed subsurface plastic deformation in single-crystal aluminum

Mechanical removal of metal induces deformation and changes to microstructural characteristics of the newly created surfaces. The mode and extent of deformation can be difficult to predict since it depends on the local crystallographic orientation, which varies significantly for polycrystalline metals. In this work, we analyzed the deformation mode and extent beneath machined surfaces of different crystallographic orientations. This was accomplished by orthogonal micromachining of single-crystal aluminum along six different crystallographic orientations orthogonal to the sample [111] zone-axis, followed by electron backscatter diffraction (EBSD) analysis to evaluate the resulting subsurface microstructure and crystal lattice rotation. The results indicate that differences in the initial material crystallographic orientation produce significant variations in the depth of deformation (compared to the uncut chip thickness), the degree of grain refinement and the extent of lattice rotations. We grouped the orientation as “hard” or “soft” based on the measured cutting force. The soft orientations exhibit deformation modes consisting of shear bands and lattice rotations; whereas hard orientations exhibit deformation modes consistent with strain hardening: localized dynamic recrystallization, highly entangled dislocations and minimal crystal lattice rotations. The depth of subsurface deformation for some orientations was extensive, reaching depths far greater than the uncut chip thicknesses. Overall, we conclude that the cutting force required to machine a given orientation does provide some insight on the local deformation mode, and orientations can be easier or harder to machine based on local susceptibility to shear and lattice rotation.

Micromachining Imposed Subsurface Plastic Deformation in Single-Crystal Aluminum

In this work, we analyzed the nature and extent of deformation beneath the machined surface during orthogonal micromachining of single-crystal aluminum. We micromachined six different crystallographic orientations of a sample with [111] zone-axis and analyzed the sub-surface texture and resulting misorientations. The results indicate that the changes in crystallographic orientation induces variations in the depth of deformation, the degree of grain refinement and the lattice rotations. We observed up to 50% lattice rotations, shear bands varying from 55o to 60o from the direction of machining, and highly entangled dislocations, which confirmed the presence of strain hardening.

Study on hole quality and surface quality of micro-drilling nickel-based single-crystal superalloy

Nickel-based single-crystal superalloy has no grain boundary. This makes the traditional cutting mechanism of shearing and slipping along grain boundary of polycrystalline material based on the theory of elastic–plastic deformation not suitable for drilling single-crystal parts. To achieve high-quality and low-damage micro-drilling of nickel-based single-crystal superalloy, the micro-drilling surface/subsurface quality of the (001) crystal plane of nickel-based single-crystal superalloy was studied in this paper. Firstly, the influence rules of the cutting speed (vs) and the feed rate (vw) on the micro-drilling hole size, surface morphology, surface roughness and subsurface damage depth were studied. Then, the micro-hardness on micro-drilling subsurface was analyzed. Finally, the subsurface recrystallization was explored. The results show that with the increase in vs, the hole diameter error and the surface roughness decrease, and the depth of subsurface plastic deformation layer decreases first and then increases; with the increase in vw, the error of hole diameter and the surface roughness increase, and the depth of the deformation layer decreases first and then increases. When vw > 0.33 μm/r, there are severe scratches on the surface of the hole wall, and the hole wall appears undulating stripes; white layer structure and severe plastic deformation layer appeared on the micro-drilling subsurface; the γ and γ’ phases' deformation is severe; the micro-hardness at the subsurface white layer is small, and the micro-hardness value at the plastic deformation zone is large; after the high-temperature treatment, γ phase dissolves on the subsurface of micro-drilling parts, and the cellular recrystallization and the complete recrystallization occur. The minimum thickness of recrystallization layer obtained is 1.43 μm at vs = 141 m/min and vw = 0.105 μm/r. This study provides a good guidance and reference for the machining of nickel-based single-crystal superalloy micro-hole parts.

Analytical and experimental investigation of improved burr morphology prediction at the top edge in metal machining

Previous research on analytical models used to predict burr size in machining operations has usually been limited to simple geometries and mechanics models. This paper investigates the material side-flow and Poisson burr formation mechanism. An improved analytical model is developed to describe the surface (subsurface) plastic deformation and Poisson burr morphology. First, the theoretical model is established based on mechanical, geometrical, and material property considerations. Then, machining experiments are performed on high-purity copper, and the proposed model is validated by comparing the predicted burr height and thickness to the experimental measurements. The results show that the developed model provides two new methods to predict burr dimensions with considerable accuracy and that this model is suitable for ductile materials. Additionally, this article offers a basis for minimizing the energy required during deburring, suppressing the formation of burrs, and optimizing the machining parameters.