Variation Of Surface Hardness Research Articles

Effect of carbon ion irradiation on the structural, mechanical and electrical properties of polycrystalline tungsten

To investigate the effects of carbon ion irradiation on the structural, mechanical and electrical properties of polycrystalline tungsten, four tungsten specimens were irradiated by 5 MeV carbon ions (C+2) at various doses ranging from 0.5 × 1015 to 3 × 1015 ions cm−2 for different exposure times. X-ray diffraction analysis confirmed the slight structural modification by increase or decrease in diffracted peak intensity, crystallite size and lattice strains upon ion irradiation. In addition, there was no substantial evidence of new phase/s in α-tungsten at high energy ions. Initially, at a lower dose rate of 0.5 × 1015 ions cm−2, the average surface hardness and electrical resistivity were found to decrease due to the increase of crystallite size. However, elevated dosed (≥1 × 1015 ions cm−2) specimens show a significant increase in their surface hardness and electrical resistivity in comparison to un-irradiated ones. The variation of surface hardness and electrical resistivity of irradiated tungsten is well correlated with crystallographic modifications, which is ascribed to the generation, recombination, augmentation, and annihilation of ion-induced defects.

Changing the characteristics of the nitrided layer using three different plasma configurations

Direct current (DC) plasma nitriding offers some disadvantages, especially in parts with complex geometries, where the presence of edges is significant, such as gears, molds, and needle punched parts are strongly affected by this effect, leading to irregular formation of nitrided layers and high variation in surface hardness. To solve these problems two techniques were developed as alternatives, namely: pulsed plasma nitriding and cathodic cage nitriding. In this work, these three nitriding techniques were compared using AISI 1045 steel as substrate. Steel discs were nitrided with the purpose of evaluating the influence of these different plasma configurations on the characteristics of the nitrided layer. The treatments in the three techniques were carried out at the same pressure, temperature, time and gas atmosphere. The samples were characterized for the microstructure, microhardness and crystalline phases present. X-ray diffraction with grazing incidence was used to verify the order of the nitrites formed and to estimate the thickness of the single-phase layers. Differences between the configurations with respect to the occurrence of restriction rings, total thickness (xe + xγ') and relative (xe/xγ') compound layers were observed. Keywords: Plasma DC; cathodic cage; pulsed plasma; nitriding; GIXRD.

Distortion control in 20MnCr5 bevel gears after liquid nitriding process to maintain precision dimensions

Robotic and automotive gears are generally very high precision components with limitations in tolerances. Bevel gears are more widely used and dimensionally very close tolerance components that need stability without any backlash or distortion for smooth and trouble free functions. Nitriding is carried out to enhance wear resistance of the surface. The aim of this paper is to reduce the distortion in liquid nitriding process, though plasma nitriding is preferred for high precision components. Various trials were conducted to optimize the process parameters, considering pre dimensional setting for nominal nitriding layer growth. Surface cleaning, suitable fixtures and stress relieving operations were also done to optimize the process. Micro structural analysis and Vickers hardness testing were carried out for analyzing the phase changes, variation in surface hardness and case depth. CNC gear testing machine was used for determining the distortion level. The presence of white layer was found for about 10-15μm in the case depth of 250± 3.5μm showing an average surface hardness of 670 HV. Hence the economical liquid nitriding process was successfully used for producing high hardness and wear resistant coating over 20MnCr5 material with less distortion and reduced secondary grinding process for dimensional control.

Influence of milling modes and tool postures on the milled surface for multi-axis finish ball-end milling

This work concentrated on the machined surface properties produced by the multi-axis ball-end milling process in order to enhance the high-performance application of multi-axis ball-end milling technology. The cutting speed of the engaged cutting edges and machining characteristics under various inclination angles were analyzed. The effects of inclination angles on the machined surface hardness, residual stresses, surface textures, topographies, and roughness were investigated under up-milling and down-milling conditions. Under up-milling condition, the machined surface hardness with regard to various tilt angles are larger than the ones under corresponding lead angles, and the variations of surface hardness with increasing lead angles are not apparent. In down-milling condition, double-peaks shape appears in the changing curve of surface hardness with increasing tilt and lead angles. The residual stresses present the overall trend of firstly increasing, then decreasing, and finally increasing with the increasing tilt angle from −45 to 45°. The surface residual stresses in both feed and cross-feed directions firstly decrease, and then increase with the increasing lead angle. Under both up-milling and down-milling, the compressive residual stresses significantly appear at the tool inclination angles near 0° due to extrusion action of the cutting edges close to tool tip and the low effective cutting speed. For down-milling condition, the surface textures are approximately parallel with the feed direction when using tilt angles with large values, and are approximately perpendicular to feed direction under varying lead angles. The apparent machining marks under negative tilt angles with relatively larger absolute values and obvious regular surface patterns corresponding to positive tilt angles could be observed. More surface pits and burrs and circular arc textures probably appear under small tilt angles and lead angles near 0°.

Spatial and temporal analysis of surface hardness across a third-generation artificial turf pitch over a year.

Despite the potentially negative effects on play performance and safety, little is currently known about the spatial and temporal variability in the properties of artificial turf pitches. The primary purpose of this study was to quantify the spatial and temporal variations in surface hardness across a 5-year-old third-generation artificial turf pitch over full year cycle. The secondary purpose was to investigate the key variables that contributed to these variations in surface hardness using a correlation approach. Surface hardness (2.25 kg Clegg impact hammer, average of drops 2–5), ground temperature and infill depth were measured at 91 locations across the third-generation artificial turf pitch in 13-monthly test sessions from August 2011 to August 2012 inclusive. For each month, rainfall in the 24 h prior to testing and pitch usage statistics were also obtained. Shockpad thickness was obtained from measurements taken when the carpet was replaced in 2007. Spatial and temporal variations were assessed using robust statistical measures while Spearman correlation was used to assess the contributions of the secondary variables to surface hardness variability. The results indicated that spatial variation in surface hardness exceeded temporal variation; the former demonstrated a median absolute deviation of 12 ± 1 G across the pitch in any test session while the median absolute deviation for the latter was only 4 ± 2 G across the 13 test sessions. Spatial variation in surface hardness was moderately correlated with shockpad thickness and weakly correlated with infill depth (both negative). These results reinforce the importance of monitoring spatial and temporal variations in play performance variables for third-generation surfaces as well as providing support for the role of maintenance in minimising the spatial variation.

Experimental and Numerical Modeling of Surface Indentation Response of Plastically Graded Materials

Materials with customized spatial gradients in mechanical properties are increasingly used in high performance applications requiring enhanced resistance to contact loads, wear, and fatigue. In many engineering materials, multiple property and microstructural gradients may occur simultaneously with depth. In this manuscript, two case carburized steels are analyzed for their gradient in hardness with depth, emphasizing the resulting variation in surface hardness under increasing indentation loads. A parametric study using finite element analysis is then conducted in order to characterize the influence of individual property gradients on the surface indentation response of graded materials. It is shown that the measured surface hardness value decreases rapidly under increasing surface indentation loads in materials with sharp negative hardness gradients. It is also shown that this trend is independent of the magnitude of the strain hardening exponent of the material, as well as the gradient in strain hardening exponent. Gradients in elastic properties were also shown to have negligible influence on surface hardness trends for a fixed gradient in hardness. Finally, it is revealed that the depth of subsurface plastic deformation increases with sharper gradients in hardness, while being insensitive to changes in strain hardening exponent. For elastically graded materials, a decreasing gradient in elastic modulus limits the depth of plastic deformation.

Effect of prestrain on and prediction of fatigue limit in carbon steel

The effect of prestrain on the fatigue limit of 0.1% (annealed) and 0.5% (quenched and tempered) carbon steel was investigated. Formulas for predicting the fatigue limit of carbon steels were proposed. The fatigue limit of 0.1% carbon steel increased with increasing surface hardness and surface compressive residual stress imposed by prestrain. The fatigue limit decreased when precracks were generated on the surface, in spite of a large surface compressive residual stress in the case of 0.5% carbon steel. The precrack, variation of surface hardness and surface residual stress were considered to be parameters applicable in formulas for predicting the fatigue limit of prestrained carbon steels. The calculated results of such formulas showed good agreement with the experimental results.

Modeling the Effects of Abrasive Size Distribution, Adhesion, and Surface Plastic Deformation on Chemical-Mechanical Polishing

A mechanical wear model for interactions between pad, wafer, and abrasives for surface removal during chemical mechanical polishing was developed. Effects of abrasive size distribution, surface softening, particle adhesion, and surface plastic deformation were included in the model. Interactions of particles that were trapped on the pad asperities with wafer surface were analyzed. Variations of surface hardness with the polishing time, down pressure, and relative velocity were also evaluated. Pads with wavy and random surface roughness were considered and model prediction results for dilute slurry concentrations were evaluated. Variations of the removal rate with down pressure, relative velocity, and surface hardness were analyzed. The results show that the surface removal rate decreases as abrasive size increases. Also for a constant relative velocity, the removal rate and the wafer surface hardness increase with increasing the slurry concentration and pressure. The results of the numerical simulations were compared with the available experimental data and good agreement was found.