Hardness properties and high-temperature wear behavior of nitrided AISI D2 tool steel, prior and after PAPVD coating

Wear experiments in the range of 25–600 °C have been conducted on samples of D2 tool steel in different conditions involving unnitrided, nitrided and nitrided and coated with Balinit^® A (TiN) and Balinit^® Futura (TiAlN) deposited industrially at Balzers (Amherst, NY, USA), by means of PAPVD. The results indicate that coating the nitrided D2 tool steel substrate with these two films gives rise to an improvement of 97% (TiN) and 99% (TiAlN) in the wear behavior at the test temperature of 300 °C, in comparison with the uncoated substrate. However, at a temperature of 600 °C, besides oxidation of the coatings, the mechanical strength of the substrate decreases giving rise to fracture and delamination of the films. At this temperature the uncoated substrate exhibited the highest resistance to sliding wear, presumably due to the formation of a well bonded surface glazed layer which gives rise to a significant reduction in the friction coefficient. The indentation experiments that were conducted with the nitrided steel substrate and the coated systems indicates that the nitriding process applied to the D2 steel prior to PAPVD coating provides a satisfactory load support which contributes to the improvement of the coated systems capability to withstand indentation loads at room temperature. In this regard, the coated system with a TiAlN coating displayed a better behavior than that shown by the system with a TiN coating. An experimental procedure is proposed in order to predict the hardness profile of the nitrided tool steel, along the cross section of the material, just from hardness measurements taken on the surface of the sample, employing different indentation loads.     

Effect of different heat treatments on the wear of high speed steel cutting tools

High speed steel tool tips were given different heat treatments to vary the microstructure, and the nature of the wear produced in turning tests was examined under the scanning electron microscope. Wear was mainly confined to either the rake face or clearance face, the form of wear being dependent on the particular heat treatment of the tool steel. The forms and mechanisms of tool wear are discussed in terms of the changes in microstructure produced by the different heat treatments.     

Friction and wear behavior of diamond-like carbon coating on plasma nitrided mild steel under boundary lubrication

The friction and wear properties of synthetic ionic liquid functionalized borate esters as additives in poly-alpha-olefin (PAO) were measured for diamond-like carbon (DLC) coating on plasma nitrided AISI 1045 steel. Results show that the borate esters gave much better friction–reduction and antiwear properties for DLC coating/steel and DLC coating/DLC coating sliding pairs than zinc dialkyldithiophosphate (ZDDP). In addition the DLC coating had much better wear resistance than the nitrided mild steel substrate, indicating that duplicate surface modification was more effective in significantly increasing the wear resistance of mild steel.     

Evaluation of gas nitriding process with in-process variation of nitriding potential for AISI H13 tool steel

Gas nitriding under controlled nitriding potential represents one of the important factors in enhancing the service life of dies used in the industry for hot aluminum extrusion. In the present study, AISI H13, a typical material used for hot extrusion dies, is gas nitrided using automated two-stage controlled nitriding process. Prior heat treatment on the material was carried out under the same controlled environment as used for hot extrusion dies to avoid any decarburization. The nitrided layer has been characterized using different techniques including optical microscopy, SEM, XRD, EDS, and microhardness analysis. It was found that controlled nitriding with in-process variation of nitriding potential can efficiently be used to control the morphology of compound layer and diffusion zone, effective case depth, case hardness, and quality of nitrided layer at sharp edges for better die performance. All the results were found in close agreement with established specifications required for improved die performance.     

Cutting forces, chip formation, and tool wear in high-speed face milling of AISI H13 steel with CBN tools

High-speed face milling experiments of AISI H13 steel (46–47 HRC) with cubic boron nitride (CBN) tools were conducted in order to identify the characteristics of cutting forces, chip formation, and tool wear in a wide range of cutting speed (200–1,200 m/min). The velocity effects are focused on in the present study. It was found that, at the cutting speed of 800 m/min, which can be considered as a critical value, relatively low mechanical load, relatively low degree of chip segmentation, and relatively long tool life can be obtained at the same time. Both the cutting forces and the degree of chip segmentation firstly decrease and then increase with the cutting speed, while the tool life exhibits the opposite trend. By means of analyzing the wear mechanisms of tools tested under different cutting speeds, it was found that, as the cutting speed increases, the influences of fracture and chipping resulting from mechanical load on tool wear were reduced, while the influences of adhesion, oxidation, and thermal crack accelerated by high cutting temperature became greater. There exist obvious correlations among cutting forces, chip formation, and tool wear.     

Evaluation of morphological and tribological properties of nanocrystalline nitrocarburised coating produced on AISI H13 carbon steel by pulsed plasma electrolytic saturation (PPES) technique

Abstract

The formation of superficial protective layers produced by pulsed plasma electrolytic saturation techniques appears to offer attractive properties in terms of wear resistance. In order to intensify the beneficial characteristics, a profound understanding of how they are affected by the processing parameters and the obtained nanocrystalline microstructure is required. In the present study, a nitrocarburised coating was produced on AISI H13 steel, and it was characterised using scanning electron microscopy and X-ray diffraction. The tribological properties of the produced coatings were evaluated using the pin on disc method. The results showed that the surface characteristics of the produced layer strongly depend on how the pulse related parameters have been applied. It was also realised that the obtained tribological properties were affected by the morphological characteristics of the produced coatings. The layers on the substrate were in the form of spherical and compact nanocrystalline nitrocarburised coatings.     

An investigation of the properties and wear behaviour of plasma-nitrided hot-working steel (H13)

The microstructural properties and wear behaviour of AISI H13 steel which had been plasma nitrided at 530 and 550 °C for times between 4 and 100 h have been investigated. The effect of treatment temperature and time on the microstructure have been examined. The wear behaviour of material treated for 4 and 100 h has also been observed. It was seen that a total case depth of 0.55 mm with a hardness of 1000 HV can be achieved in 100 h. However, the white layer thickness is increased to 17 μm while the core hardness is reduced to 480 HV at 550 °C. The wear rate of the sample treated at 550 °C for 100 h is higher than that of the sample treated at 550 °C for 4 h.     

An investigation of heat partition and tool wear in hard turning of H13 tool steel with CBN cutting tools

This paper presents results of an investigation into the tool life and the tool wear behaviour of low content CBN cutting tools used in hard turning of hardened H13 tool steel. The approach followed here required both experimental work and finite element thermal modelling. The experiments involved measuring the cutting forces, cutting temperatures, tool wear, and the contact area. Using the measured cutting forces and the contact area in the orthogonal cutting model, we calculated the heat flux on the tool and applied it in the FE thermal analysis. The temperatures history from the analysis was matched with the experimental data to estimate the fraction of heat entering the tool for both conventional and high speeds. The heat partition into the tool was estimated to be around 21–22% for conventional speeds, whereas for high-speed turning, it was around 14%. The tool wear, however, was found to be dominated by chipping for both cutting speeds and could be reduced considerably by reducing the amount of heat entering the tool.     

Micro-scale abrasive wear testing of duplex and non-duplex (single-layered) PVD (Ti,Al)N, TiN and Cr–N coatings

A micro-scale abrasive wear test, based on ball-cratering, has been used to evaluate the wear resistance of duplex and non-duplex (Ti,Al)N, TiN and Cr–N coatings. The term duplex is used here when plasma nitriding is followed by PVD coating. Coatings without the plasma nitriding stage are termed single-layered. Coating properties were evaluated by surface profilometry, hardness and scratch testing. All duplex coatings showed higher micro-abrasive wear resistance than their single-layered counterparts, with the duplex (Ti,Al)N coating achieving the best performance. After a certain number of ball revolutions, the coating material became worn through, exposing the substrate material. After this point, the presence of a hard nitrided case diminished the scratching action of the SiC abrasive particles. The experimental results also indicate that the choice of the PVD coating plays an important role in improving the micro-abrasive wear resistance. Apart from single-layered and duplex Cr–N coatings, all the other coating systems provided a higher micro-abrasive wear resistance than the uncoated substrate (hardened AISI H13 steel). The poor abrasive wear resistance recorded for the single-layered and duplex Cr–N coatings could be attributed to the hardness of the Cr–N being much lower than that of the SiC abrasive particles, which caused tearing of the coating with subsequent delamination. The wear pattern observed was found to change from surfaces characterised by grooves (uncoated substrate, single-layered TiN and Cr–N systems and duplex Cr–N system) to surfaces which exhibited multiply indented surfaces (single-layered and duplex (Ti,Al)N systems), indicating a transition between wear mechanisms. This transition was found to be dependent on the ratio between the hardness of the SiC abrasive particles and surface (coating) or subsurface hardness. By decreasing this ratio, the ability of the SiC abrasive particles to scratch the composite surface was reduced and the resistance to micro-scale abrasion was improved.     

Study on relative wear resistance and wear stability of high-speed steel with high vanadium content

In this work, a new concept of wear stability was put forward by authors, and it was quantitatively expressed by factor of wear stability. Different hardness, impact toughness and retained austenite content high-speed steel with high vanadium content samples were obtained by varying heat treatment conditions. The effects of hardness, impact toughness and retained austenite content on relatively wear resistance and wear stability were studied under abrasive wear condition. Results show that relative wear resistance increases with increasing hardness or decreasing impact toughness, whereas the wear stability rises with the increasing of hardness or impact toughness. The analyzing results reveal that mechanical behaviors are only apparent factors to influence wear behaviors. Relative wear resistance substantially depends on retained austenite content (Ar). At retained austenite content of about 30 vol.%, the relative wear resistance is optimal. However, wear stability is scarcely influenced by retained austenite content, which depends on the maximum changing amount of retained austenite under certain condition (ΔAr) in essence. With increasing ΔAr, wear stability linearly decreases.     

The effect of microstructure and wear conditions on the wear resistance of steel metal matrix composites fabricated with PTA alloying technique

The concept of hard particles in a softer metal matrix has long appealed to number of industries dealing among others with drilling and mining. For these facilities, the PTA (Plasma Transferred Arc) alloying technique is advisable and advantageous for several reasons; the equipment may be portable and moved near the working site, the treatment may be applied strictly to the area where the wear problem is situated and after the treatment little machining is required. Four different coatings are tested against three different modes of wear occurring either alone or less frequently combined in this kind of applications, i.e. adhesion, low stress abrasion and two-body abrasion. Two of the coatings examined belong to the category of tool steels with very hard carbides in their microstructure, namely TiC, M₂C and M₆C. The other two are boride coatings belonging to the Fe–B and Fe–Cr–B system respectively. A heat treated AISI D2 tool steel commonly used in this type of applications is also examined for comparison. Fe–Cr–B coating performance is at least 2 times better in low stress and two-body abrasion and four orders of magnitude better in adhesion wear than the AISI D2 tool steel. Fe–B coating can be used in pure adhesion or abrasion situations, but their brittleness forbids their use in situations involving impact loading. AISI M2 coating presents similar wear performance with AISI D2 tool steel in abrasion, whereas in adhesion wear it performs at least two orders of magnitude better. MMC–TiC coating has good performance in pure two-body abrasion situations due to the presence of the very hard TiC particles in its microstructure.     

Effects of cutting edge geometry, workpiece hardness, feed rate and cutting speed on surface roughness and forces in finish turning of hardened AISI H13 steel

In this study, the effects of cutting edge geometry, workpiece hardness, feed rate and cutting speed on surface roughness and resultant forces in the finish hard turning of AISI H13 steel were experimentally investigated. Cubic boron nitrite inserts with two distinct edge preparations and through-hardened AISI H13 steel bars were used. Four-factor (hardness, edge geometry, feed rate and cutting speed) two-level fractional experiments were conducted and statistical analysis of variance was performed. During hard turning experiments, three components of tool forces and roughness of the machined surface were measured. This study shows that the effects of workpiece hardness, cutting edge geometry, feed rate and cutting speed on surface roughness are statistically significant. The effects of two-factor interactions of the edge geometry and the workpiece hardness, the edge geometry and the feed rate, and the cutting speed and feed rate also appeared to be important. Especially honed edge geometry and lower workpiece surface hardness resulted in better surface roughness. Cutting-edge geometry, workpiece hardness and cutting speed are found to be affecting force components. The lower workpiece surface hardness and honed edge geometry resulted in lower tangential and radial forces.     

Effect of electro discharge machining (EDM) on the AISI316L SS white layer microstructure and corrosion resistance

The localised corrosion resistance of austenitic stainless steels is strongly influenced by the quality of finished surface. EDM machining induces substantial changes by the high thermal gradients generated by electric sparks. Experimental techniques such as roughness measurement, scanning electron microscopy (SEM), energy dispersive microanalysis (EDX) and X-ray diffraction technique, reveal micro-geometrical, microstructural, chemical and mechanical changes. These changes lead to white and heat-affected layers with a depth less than 100 μm. The white layer is a melted material characterised by dendritic structure and constituted by austenite, chromium carbide and ε-carbide. The heat-affected layer is characterised by very large grain size comparatively to the bulk material. Electrochemical test coupled with metallographic examinations using SEM reveals a weakening of the resistance to pitting and intergranular corrosion comparatively to diamond polished surface. This weakening is correlated to differences in structure and chemical composition of white layer. Susceptibility to stress corrosion cracking has been attributed to the field of tensile residual stresses resulting from thermal effects. The removal of the white layer material by polishing or wire brushing restores the corrosion resistance of the AISI316L SS.     

Experimental investigation on deformation and wear of WC tool during friction stir welding (FSW) of stainless steel

In this paper, the effect of friction stir welding (FSW) parameters on wear and deformation behavior of tungsten carbide (WC) tool employed in the welding of AISI 304 austenitic stainless steel (SS) is reported. In addition, the wear and deformation of the tool are also characterized. Three FSW parameters, namely shoulder diameter, tool rpm, and traverse speed each at three levels were considered. Experiments were performed as per Taguchi’s L₉ orthogonal array to investigate the effect of these parameters on wear and plastic deformation of the tool. Wear at the pin root and bottom face of the pin attributed to diffusion and attrition mechanisms, respectively, were observed. Significant deformation of the tool was also observed during welding which caused bulging of the shoulder with an increased cone angle of the pin.     

Comparative study on tool life and wear resistance of titanium nitride (TiN) and aluminium chromium nitride (AlCrN) coated carbide inserts

Abstract

The objective of this study is to investigate the enhancement of tool life and wear resistance with a physical vapour deposition (PVD) process applied using aluminium chromium nitride (AlCrN) and titanium nitride (TiN) coating on carbide inserts. Flank wear experiments are carried out on a computer numerically controlled (CNC) machine under wet conditions with both the coated inserts. Effectiveness of the coating on the tool life and its resistance to flank wear are observed at various cutting parameters such as cutting speed and feed rate by following the principle of design of experiments (DOE). It is inferred that AlCrN coated carbide tools perform nearly 70% better than the TiN coated carbide tools under high cutting speed and feed rate. AlCrN coating also enhances the durability of tool for metal cutting and thereby improves tool life even under harsh cutting conditions. A response surface methodology (RSM) is utilised to arrive at the optimum value for the various parameters which are responsible for improving the wear resistance and tool life.     

Effect of the specimen geometry on wear - combination of polyacetal (POM) and carbon steel for machine structures

Engineering plastics which have been shown to have good mechanical properties are now frequently used as materials for various machine elements. Engineering plastics are combined with other engineering plastics and metallic materials for machine construction. These machine elements are fabricated with contact surface forms, such as convex, concave, and plane surfaces. Therefore, when designing machines with a combination of materials containing engineering plastics, it is useful to know the wear and friction characteristics for various contact surface forms. In the present research, polyacetal (POM), an engineering plastic, and carbon steel, a metal often used for machine structures, were chosen as materials to study wear and friction. Wear tests were performed in the combination of a convex surface and a plane, and in the combination of a plane and a plane. As a result, some features of the wear and friction characteristic are clarified. (1) The worn mass when the flat specimen made of POM is rubbed by the POM pin specimen is larger than when with the pin specimen made of carbon steel. (2) When the flat specimen made of POM is rubbed by the POM or the carbon steel pin specimen, the same grade of wear is observed regardless of the pin specimen material. (3) The worn length of the steel spherical pin specimen on the steel flat specimen becomes close to the initial radius of the curvature of the pin specimen when the sliding distance is large. The initial condition of the spherical tip pin specimen on the flat specimen evolves toward a condition of the flat tip pin specimen on the flat specimen. So, the comparison between the two geometries is non-relevant. Such problem did not occur in POM pin specimen.     

Effect of bulk heat treatment and plasma surface hardening on the microstructure and erosion wear resistance of complex-alloyed cast irons with spheroidal vanadium carbides

The results of an investigation of the effect of bulk quenching from temperature in the range of 760–1050°C, cryogenic treatment (–196°C) and surface plasma hardening on the abrasive-erosion wear of frugally alloyed V–Cr–Mn–Ni cast irons with spheroidal vanadium carbides have been presented in this article. It has been found that cast irons containing 5.0–7.5% V, 4.5–9.0% Cr, and 5.5–5.7% (total) of Mn and Ni after heat treatment have a 2–3-fold advantage in wear resistance compared to the prototype high-vanadium cast iron (11.9% V, 12.9% Mn). The maximum wear resistance of cast irons studied is achieved by quenching at 760°C followed by plasma surface hardening, as well as quenching at 840°C, followed by cryogenic treatment. These treatments result in the formation of an optimum microstructure that consists of spheroidal vanadium carbides, eutectic carbides M₇C₃, and a martensite-austenite matrix reinforced by secondary carbides. The increase in quenching temperature leads to an increase in the amount of residual austenite and decrease in the erosive wear resistance of cast irons.     

Effects of sliding velocity and normal load on friction and wear characteristics of multi-layered diamond-like carbon (DLC) coating prepared by reactive sputtering

Friction and wear tests were performed to investigate effects of sliding velocity and normal load on tribological characteristics of a multi-layered diamond-like carbon (DLC) coating for machine elements. The DLC coatings which consist of sequentially deposited gradient Cr/CrN, W-doped DLC (a-C:H:W) and DLC (a-C:H) layers were formed on carburized SCM 415 Cr–Mo steel disks using a reactive sputtering system. The tests against AISI 52100 steel balls were performed under various sliding velocities (0.0625, 0.125, 0.25, 0.5, 1 and 2 m/s) and normal loads (6.1, 20.7 and 49.0 N) in ambient air (relative humidity=26±2%, temperature=18±2 °C). Each test was conducted for 20 km sliding distance without lubricating oil. The results show that friction coefficients decrease with the increase in sliding velocity and normal load. Wear rates of both surfaces decrease with the increase in normal load. The increase in sliding velocity leads initially to the increase in wear rates up to the maximum value. Then, they decrease, as the sliding velocity increases above specific value that corresponds to the maximum wear rate. Through surface observation and analysis, it is confirmed that formation of transfer layers and graphitized degree of wear surfaces of DLC coatings mainly affect its tribological characteristics.     

Grey theory applied to evaluate the tribological performances of the a-C:H(N) coating films prepared by differing the nitrogen content and the film thickness

The purpose of this paper is to study the tribology performances of the aC:H(N) films by using a nanotester under different scratch loads and velocities. From the measurements of the friction coefficient and wear volume, the tribological performances including wear resistance and friction coefficients were evaluated for the hydrogenated amorphous carbon films prepared by differing film thickness and nitrogen volume friction in the gas mixture of (C₂H₂+N₂). Taguchi experimental design and the grey relational analysis were used to investigate the influence of specimen parameters (film’s thickness, nitrogen content in the film), and operating conditions in tribological tests (scratch load and scratch velocity) on the friction coefficients and the wear volume arising in the specimens with different coating films. It is found that the wear volume of thin film is increased by increasing either the nitrogen volume fraction or film thickness. Moreover, the optimal combination of the testing parameters was also determined in the use of the present model.     

Effect of the reinforcement (carbon or glass fibres) on friction and wear behaviour of the PEEK against steel surface at long dry sliding

PEEK (poly-ether-ether-ketone) is a high performance engineering semicrystalline thermoplastic. PEEK has excellent tribological behaviour, which is optimised in the specially formulated tribological composite grade.This paper presents a comparative study of wear and friction on PEEK, PEEK-CF30 (wt%) and PEEK-GF30 (wt%) against steel, at long dry sliding. A plan of experiments was performed on a pin-on-disc machine, under the following conditions $pv=2\text{MPa}\text{m/s}$ (p = 8 MPa and $v=0.25\text{m/s}$; p = 2.68 MPa and $v=0.75\text{m}\text{/}\text{s}$) at the ambient temperature for a sliding distance of 15 km.PEEK-CF30 presented the lesser friction coefficient followed by PEEK. PEEK-GF30 presented the higher friction coefficient throughout all sliding distance. Both PEEK-CF30 and PEEK-GF30 have presented an excellent wear resistance relatively to PEEK while PEEK-CF30 presented the best tribological behaviour.