M2 Tool Research Articles

Lubrication of Steel/Steel Contacts by Choline Chloride Ionic Liquids

There is a growing interest in the use of ionic liquids to provide lubrication for challenging contacts. This study is an initial assessment of the application of two ionic liquids based on choline chloride cations to be used as ionic liquid lubricants for engineering contacts, in this case steel on steel. These ionic liquids, termed ethaline and reline, have anions of ethylene glycol and urea, respectively, and are available at relatively low costs and in high quantities. In order to assess the lubrication performance of the ionic liquids, lubricated reciprocating sliding wear tests were conducted between M2 tool steel samples and a steel stylus. Initial tests conducted at a sliding speed of 0.005 m s−1 and 30 N showed that ionic liquids could provide low friction lubrication, comparable to that of SAE 5W30 friction modifier free engine oil under the same test conditions; however, lubrication was lost after short sliding distances. Further testing with higher sliding speed/lower load and varying sample surface textures showed that ionic liquid lubrication could be better maintained in high-speed/low-load testing and by increasing the roughness and therefore surface area of the sample. It was also observed that the choline chloride/urea ionic liquid formed a residual film when tested on iron silicate peened samples, and that this film may promote lubrication.

Investigation of the adhesion of NbN coatings deposited by pulsed dc reactive magnetron sputtering using scratch tests

Scratch tests have been used to investigate the adhesion of niobium nitride (NbN) coatings that were deposited by pulsed dc reactive magnetron sputtering at target currents of 1.5, 2.5, and 3.5 A onto M2 tool steel and silicon wafer. The coating adhesion on each material substrate was investigated using a progressive load scratch tester (PLST) and a multi-pass scratch tester (MPST). Microhardness tests and scanning electron microscopy (SEM) were also used to examine the hardness and microstructure of the NbN coatings. These results have indicated that the structural, mechanical, and adhesion properties of the NbN coatings improve with increasing target currents. While performing PLST and MPST tests, the highest adhesion and lowest friction force were obtained for the coatings deposited at a target current of 3.5 A. In addition, the triboscobic behaviors that were observed from the MPST of the coatings indicated that the target currents affect the friction behavior of the coatings.

Effects of CPII implantation on the characteristics of diamond-like carbon films

A diamond-like carbon film (DLC) was successfully synthesized using a hybrid PVD process, involving a filter arc deposition source (FAD) and a carbon plasma ion implanter (CPII). A quarter-torus plasma duct filter markedly reduced the density of the macro-particles. Graphite targets were used in FAD. Large electron and ion energies generated from the plasma duct facilitate the activation of carbon plasma and the deposition of high-quality DLC films. M2 tool steel was pre-implanted with 45 kV carbon ions before the DLC was deposited to enhance the adhesive and surface properties of the film. The ion mixing effect, the induction of residual stress and the phase transformation at the interface were significantly improved. The hardness of the DLC increased to 47.7 GPa and 56.5 GPa, and the wear life was prolonged to over 70 km with implantation fluences of 1 × 10 17 ions/cm 2 and 2 × 10 17 ions/cm 2, respectively.

Erosive wear of hardfaced Fe–Cr–C alloys at elevated temperature

Many engineering components are subjected to erosive wear at elevated temperature. As erosive wear at elevated temperature is governed by the synergistic effect of erosive wear and oxidation, it is possible to modify surfaces of the components in order to achieve improved performances. In view of the above, two different types of hardfacing alloys of Fe–Cr–C were designed incorporating Nb, Mo and B to ensure improved performances at elevated temperature. In order to achieve the above objective, mild steel was hardfaced with these alloys under optimised gas metal arc welding (GMAW) condition. The microstructures of the hardfaced coating was characterised with the help of optical microscopy (OM) and scanning electron microscopy (SEM). The mechanical properties of these coatings were obtained by means of micro indenter. Erosive wear of these coatings was evaluated for four different temperatures, for two different impact angles and at one impact velocity. The morphologies and the transverse sections of the worn surfaces are examined with SEM. The erosive wear of these coatings were compared with conventional M2 tool steel. Results indicate that erosion rate of these coatings increases with increase of test temperature and impact angles. Among various coatings, Fe–Cr–C coating containing higher amount of Nb, Mo and B exhibits best erosion resistance particularly at elevated temperature.

Solid–liquid structural break-up in M2 tool steel for semi-solid metal processing

The success of semi-solid metal processing mostly depends on the formation of suitable starting microstructure, which must consist of solid metal spheroids in a liquid matrix. Various methods of obtaining this structure have been established; they include recrystallisation and partial melting (RAP), strain-induced melt-activated (SIMA), or simple mechanical stirring, to name a few. These methods, as widely discussed, have mostly been applied with light alloys, mainly aluminium based. This article discusses solid–liquid structural break-up in M2 tool steel subjected to a direct re-melting procedure from the as-annealed condition. The role of carbide dissolution in the grain boundary liquation of the steel is described. This leads to the production of near spheroidal solid grains in a liquid matrix, a microstructure suitable for the thixoforming process. Microstructural examination revealed that carbide particles contained in bands at 1220 °C slowly disappeared with temperature. At 1300 °C, the solid grains seemed to be free from carbides. Most of the carbides had now re-precipitated at the grain boundaries. Thixoforming carried out at 1340 and 1360 °C revealed the thixotropic properties of the semi-solid metal slurries. The results indicate a widening of the range of potential routes to thixoformable microstructures.

A study on the abrasive and erosive wear behavior of arc-deposited Cr–N–O coatings on tool steel

In this study, the cathodic arc evaporation technique, by using the chromium target and controlling the flow rate of nitrogen/oxygen reactive gases, was utilized to deposit three different Cr–N–O coatings (CrN, CrN/Cr(N,O), CrN/Cr 2O 3) on AISI M2 tool steel. Two types of wear tests were applied to evaluate the abrasive and erosive wear behavior of the coated and uncoated specimens. One was the ball-on-disk abrasion test to measure the friction coefficient of these specimens. The other was the erosion test using Al 2O 3 particles (~ 177 µm in size and Mohr 7 scale) of about 5 g, and then the surface morphologies of the eroded specimens were observed. To further understand the coating effects on the two wear behaviors of M2 steel, coating structure, morphology, and adhesion were analyzed using XRD, SEM, and TEM, respectively. The results showed that surface roughness and adhesion of the double-layered coatings (CrN/Cr(N,O) and CrN/Cr 2O 3) were inferior to those of monolithic CrN, but their hardness and elastic modulus were superior to those of CrN. In the abrasive behavior, Cr–N–O coatings reduced the friction coefficient of M2 substrate. In particular, the CrN/Cr 2O 3 has the highest hardness/elastic (H/E) modulus ration, therefore the lowest friction coefficient, among all the coated-specimens tested. In the erosive behavior, the coated specimens exhibited better erosion resistance as compared to the uncoated ones, at the impingement angles of either 30 o or 90 o. Moreover, the erosion resistance of CrN/Cr(N,O) coatings was superior to that of CrN/Cr 2O 3 coatings due to its better adhesion.

Corrosion Resistance of Tool Steel Arc-Deposited Cr-N-O Double-Layered Coatings in 3.5% Sodium Chloride

Abstract In this study, the cathodic arc deposition technique was utilized to synthesize three Cr-N-O coatings (chromium nitride [CrN], CrN/Cr[N,O], CrN/chromium oxide [Cr2O3]) on AISI M2 tool steel by using the chromium target and controlling the flow rate of nitrogen/oxygen reactive gases. Polarization tests were performed to evaluate the corrosion resistance of the uncoated and coated specimens in 3.5 wt% sodium chloride (NaCl) solution. Structure and morphology of the coatings were separately analyzed using x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to better understand the coating effects on the corrosive behavior of M2 steel. The results showed that the CrN/Cr(N,O) and CrN/Cr2O3 double-layered coatings had higher surface roughness than monolithic CrN, but their dense and double-layered structures resulted in better corrosion resistance. The sequence of corrosion resistance is in the order of CrN/Cr(N,O) > CrN/Cr2O3 > CrN > uncoated M2 stee...

Analysis of Rheological Properties of Steel near Solidus Point Using Gleeble<sup>®</sup> Simulator

The main goal of this work is the analysis of rheological properties of steel alloy at high temperatures, just below the solidus point, and in the semi-solid state with low liquid phase content. Data obtained from the analysis can form the basis of numerical simulation for designing and optimizing the thixoforming processes. The rheological properties should be known over a wide temperature range so that the simulations could also predict defects such as incomplete die filling. The analysis concerned M2 tool steel alloy. The paper also discusses development of globular microstructure in partially melted steel.

Atomic transport and chemical reaction in TiN/Ti nanolayers on plasma nitrided steel

Transport of N, O, and Ti during dc magnetron sputtering deposition of nanoscopic TiN/Ti and TiN structures on plasma nitrided M2 tool steel, as well as transport of metallic species composing the plasma nitrided steel substrates were investigated. N and O depth distributions were determined with subnanometric resolution using narrow resonant nuclear reaction profiling, whereas Ti was profiled, also with subnanometric depth resolution, by medium energy ion scattering. The surface elementary compositions of the TiN/Ti/nitrided steel and TiN/nitrided steel structures were determined by low energy ion scattering. The chemical compounds formed during deposition were accessed by X-ray photoelectron spectroscopy, indicating the presence of TiN, TiO2, Ti oxynitrides, as well as other metallic nitrides and oxynitrides, but no metallic Ti was observed. Owing to the observed intensive atom mobility, the compositions of the deposited films on plasma nitrided steel structures varied continuously on a nanoscopic scale, from the core of the steel substrate to the bulk of the stoichiometric TiN films. The Ti interlayer assists interdiffusion of all species, in contrast to the TiN film layer, which is known to be a diffusion barrier. The improved adhesion of TiN hard coatings to plasma nitrided steel under working conditions is discussed in terms of the gradual compositional change around the interfaces and the atomic mobility during their formation.

Material transfer phenomena and failure mechanisms of a nanostructured Cr–Al–N coating in laboratory wear tests and an industrial punch tool application

In this research, CrAlN and TiN coatings were deposited on AISI M2 tool steel substrate test coupons and on industrial punch tools by electron beam plasma-assisted physical vapour deposition (EB-PAPVD). The microstructure and morphology of the coatings were investigated by XRD, XPS, TEM, and SEM with EDX. Pin-on-disc tribotests were conducted on the coatings against AISI 52100 steel counterface material in order to investigate their wear performance, with particular emphasis on the material transfer phenomena during the sliding tests. After industrial trials on piercing high strength steels, the worn uncoated as well as CrAlN- and TiN-coated punches were also studied. The results showed that the nanostructured CrAlN coating exhibited less material transfer and thus better adhesive wear protection than the TiN coating under both laboratory pin-on-disc tribotests and industrial trial conditions. It was also found that the coating morphologies replicated the surface finish of the punch substrates, and that local coating spallation appeared to be initiated at machining grooves on the punches, which were detrimental to the coating lifetime.

Analysis of the heating process and development of a microstructure suitable for thixoforming of steel

The thixoforming processes of metal alloys are carried out in the semi-solid state. The thixotropy phenomenon is conditional upon the globular microstructure that occurs in shaped material. In order to design and optimise such processes, some procedures of the Gleeble® system could be applied. The main objective of this work is an analysis of the resistance heating of samples in different material tests which are possible on the Gleeble® 3800 simulator. An example of development of steel alloy microstructure during heating on the Gleeble® simulator will also be presented. M2 tool steel was submitted for analysis. In this case, obtaining the globular microstructure was carried out on the basis of the SIMA method (Strain Induced Melt Activated).

A comparative study of mechanically mixed layers (MMLs) characteristics of commercial aluminium alloys sliding against alumina and steel sliders

Dry sliding of four commercial wrought aluminium alloys; AAA2124, AAA3004, AAA5056 and AAA6092 against two different materials (M2 tool steel and a high purity alumina) at room temperature were carried out. A ferrous slider was used, to promote a mechanically mixed layer (MML). It was found that in Al/M2 tests, the presence of major alloying elements in the Al-alloy that have high solubility in steel promoted a thick mechanically mixed layer. The solubility of these elements in α-Fe is in the order of Si, Mn, Cu, Mg, which roughly approximates the thickness of the MML formed, while the Fe content of the MML also scaled in this order. The MMLs with high Fe content tended to be comprised of fragmented particulate, while a low Fe content tended to be associated with a more homogenous MML. As for the Al/Al 2 O 3 tests, the MML was derived from fracture of the slider, and also from transfer and re-transfer of the aluminium alloy. An alumina slider was used, in principal, to minimise the formation of an MML, so that the true effect of the work hardening induced by wear can be analysed. In contrast to the Al/M2 tests, none of the alloying elements in the aluminium alloy were expected to chemically react with the Al 2 O 3 , but the thickness of the MML appears to be controlled by different factors to that against the M2 slider. Detailed analyses of the wear performance and the work hardening effects were also undertaken in order to explain the differences between the tests.

An investigation of the densification and microstructural evolution of M2/316L stepwise graded composite during co-sintering

The densification and microstructural evolution during co-sintering of M2 tool steel/316L stainless steel composite layers with and without boron addition was studied. A pressureless sintering method in conjunction with a powder layering technique was used to fabricate the stepwise graded composite layers. Isothermal and non-isothermal sintering response of the individual and composite layers was examined and the microstructural features of the bonding zone were studied. Shear strength and microhardness of the bonding zone were also measured. It was shown that an enhanced densification is obtained in the composite layers due to (i) sintering shrinkage incompatibility between two steels, (ii) interlayer diffusion of the alloying elements and formation of a dual δ-ferrite/austenite phase at high temperature, and (iii) formation of a low temperature eutectic Fe (C)-B phase at the interface in the samples containing boron. The morphology of carbides in M2/316L is significantly changed as the sintering temperature increases, i.e., they appeared as fine intergranular carbides at low temperatures (1,240 °C), thick film at 1,260 °C and herringbone shape eutectic at 1,290 °C. Elongated grains with an intergranular boride phase were seen in the bonding zone of M2/316L + B layers. The shear strength of the interface of the composite layers was found to be superior to that of the individual layers.

Influence of bias voltages on the structure and wear properties of TiSiN coating synthesized by cathodic arc plasma evaporation

Nanocomposite TiSiN films have been deposited on M2 tool steel substrates using TiSi alloy as target by a dual cathodic arc plasma deposition (CAPD) system. The influences of bias voltages on the microstructure, mechanical and tribological properties of the films were investigated. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction techniques were employed to analyse the microstructure, grain size and residual stress. Nano-indentation and tribometer testers were used to measure the mechanical and tribological properties of nanocomposite TiSiN thin films. The results showed that the hardness of the films ranged from 25 to 37 GPa, which were higher than that of TiN (21 GPa). The coefficient of friction of the TiSiN thin films was more stable but was higher than that of TiN when wear against both Cr steel and WC-Co ball, respectively. When encountered with both Cr steel and WC-Co ball of the counter ball, the tribological mechanisms of TiSiN thin films are adhesive and abrasion wears, respectively. It has been found that the microstructure, mechanical and wear properties of the films were correlated to bias voltage, grain size, and amorphous Si 3N 4 nanocomposite formed in film structure, resulting in a superhard TiSiN coating.

Studies on the fabrication of tool steel components with micro-features by PIM

Fabrication of structures with fine features has been a challenge and has required sophisticated equipment. In the current work, the use of a cost-effective method, PIM (powder injection molding) was evaluated to fabricate structures with fine features such as sharp edges with dimension in microns. The selected component consisted of micro features of two steps having a cross-section dimension of 0.6×0.07 mm and 0.6×0.06 mm. In order to achieve good mechanical properties coupled with wear resistance, an M2 tool steel material was selected. The mould tip region with two-step micro features was fabricated using into multi-mould pieces to ensure the edge sharpness of the two-step micro features in the mould cavity and to create an air vent to release the entrapped gas at the moulding stage. The moulded samples were first debound and then sintered at different temperatures. The results of actual sintering at 1,244, 1,252, 1,260, and 1,280°C were analyzed, since transition to liquid phase sintering occurs in this region. Visual observation, microstructural analysis and hardness distribution were carried out on the samples sintering at different temperatures. Incomplete sintering occurred at 1,244°C while at 1,252°C distortion of the samples was identified. Sintering at 1,260°C yielded parts with good integrity and strength and a further increase of sintering temperature deteriorated the characteristics. Five samples were chosen randomly from three batches of 100 pieces for a pilot production scale. Their dimensional flatness was measured and the result showed that flatness less than ±0.3% can be achieved under optimized sintering temperature of 1,260°C ± 0.3°C. This means that the M2 tool steel component with micro features can be possibly produced by PIM process in mass production.

Relationship between test severity and wear mode transition in micro-abrasive wear tests

Recently, the micro-scale abrasive wear test has gained large acceptance in universities and research centers, being widely used in studies on the abrasive wear of materials. The purpose of this work is to relate a quantity called test severity ( S test) with the abrasive wear mode transition. The analysis took into consideration the hardness of the materials; the contact pressure ( P) between the specimen and the ball and the equipment configuration (fixed-ball or free-ball). Tests were conducted with balls of AISI 52100 steel and specimens of ISO P20 cemented carbide (WC-Co) and AISI M2 tool steel. The abrasive slurry was prepared with black silicon carbide (SiC) particles (average particle size of 5 μm) and distilled water. The results were analyzed in plots of S test and A g/ A p as a function of test time ( t) and V as a function of P, where A g is the projected area fraction with grooving abrasion; A p the total projected area and V is the volume of the worn crater. The results allowed observing that the value of S test decreased from the beginning to the end of all tests. When the results obtained with fixed-ball and free-ball equipment were compared, this decrease in S test was similar in the case of the WC-Co specimen, for which the hardness of the specimen ( H s) was larger than the hardness of the ball ( H b). The decrease in S test was different in the case of the AISI M2 specimen, for which H s < H b. Tests were also associated with a decrease in the ratio A g/ A p as a function of test time. A transition from mixed mode into pure rolling abrasion occurred at similar test times in the cases with similar severity evolution and, for the AISI M2 specimen, occurred earlier for the condition with lower test severity.

Micromachining M2 tool steel using nanostructured titanium-doped cutting tools

Cation-substituted Til-x-y-zAlxCryY2N alloys, with y = 0.03 and z = 0.02, have been shown to offer enhanced high-temperature oxidation resistance compared to presently used TiN and Til-xAlxN films. Layers (3 m thickness) were deposited by unbalanced magnetron sputter deposition to small grain WC-Co unused cutting tools which had been ion etched in situ using a steered Cr-metal-ion cathodic arc discharge at an Ar pressure of 6 10-4 mbar (0.45 mTorr). Machining experiments conducted at the meso and micro scales indicated that cutting tool life is improved significantly using yttrium-doped titanium-based coatings when machining M2 tool steel.

Improvement of the tribological behaviour of PVD nanostratified TiN/CrN coatings — An explanation

A hard TiN/CrN multilayered coating, consisting of alternating nanometer scale TiN and CrN layers (bilayer period of 40 nm), was deposited by arc evaporation process on M2 tool steel. Monolayered TiN and CrN are also deposited in the same conditions, and used as references. In order to get a better understanding of the tribological behaviour of coated parts, two types of experiments were performed. The dry-sliding wear resistance was evaluated with a ball-on-disk tribometer, while surface fatigue resistance was determined by a cyclic multi-impact test. The architecture of layers is measured by XRD and observed by TEM. The residual stress field was characterised using XRD and the sin 2 ψ method at a synchrotron radiation facility. All coatings present a columnar microstructure. TiN demonstrated better wear resistance than CrN and this characteristic is still increased two times by using the nanostratified coating. In the same way, the results of surface oligo-cyclic fatigue test confirm the high performance of the nanostructured coating with respect to the monolayered ones. The differences in mechanical properties of coatings evaluated through nanoindentation measurements do not lead to a direct correlation with the tribological results, and therefore cannot explain such differences. Moreover, a microscopic analysis of the samples after both tribological tests reveals two opposite cracking mechanisms. Monolayered TiN and CrN are subjected to a transversal crack propagation until the peeling of the coating, whereas the multilayered coating only undergoes cohesive cracks deviated in the TiN/CrN interface zones. Both opposite behaviours are the consequence of the distribution of stresses along the thickness of the film.

Further studies in selective laser melting of stainless and tool steel powders

Previous reported work on the selective laser melting of a H13 tool steel powder bed surface has shown that there is a scan speed range in which the layer mass increases/fluctuates with increasing speed. This paper expands the investigation towards M2 tool steel and 316L stainless steel powders to identify if they reveal similar behaviours. Wide ranges of scan spacings and scan speeds have been examined, at selected laser powers. Furthermore, the masses of the layers have been compared with those predicted from an existing finite element thermal model. It has been found that at a constant laser power, the variation of mass with scan speed is much less than might be expected from a constant assumed absorptivity into a powder bed.

Effects of titanium-implanted pre-treatments on the residual stress of TiN coatings on high-speed steel substrates

This investigation examined how titanium ion implantation pre-treatment affects the residual stress of TiN coatings on M2 high-speed steel. Ions were implanted by metal plasma ion implantation. The adhesion strength of the TiN coatings was enhanced by pre-treatment that implanted Ti into the M2 tool steel substrate. The implanted substrate functioned as a buffer layer between the deposited TiN and the tool steel substrate, resulting in variations of the residual stress. The residual stress determined by glancing-angle XRD demonstrates that the deposited TiN films on ion-implanted substrates exhibited reduced compressive stress, from − 3.95 to − 2.41 GPa, which corresponded to a decrease in the grain size of the TiN films. The texture of the TiN film was clearly transformed from the preferred orientation of (220) to (111), subsequently enhancing wear resistance against a tungsten ball.