Investigation of the diamond machinability of newly developed hard coatings

Presently, coatings of electroless nickel are used for diamond turning molds for injection molding of optical lenses. We have investigated the diamond machinability of substoichiometric hard nitride coatings (TiN_x, TiAlN_x, and CrN_x). These coatings have a superior hardness compared to electroless nickel suggesting an improved wear resistance of molds with optical surface quality. In the case of CrN_x and TiAlN_x, high tool wear occurred, even after small cutting distances, and the surfaces showed a roughness larger than R_a = 0.5 μm. A considerably higher surface quality was obtained on TiN_x coatings. The best results (R_a = 15 nm) were achieved with a nitrogen content of x = 0.03. As a first application, a mold for a diffractive optical element was machined using this newly developed substoichiometric titanium nitride deposit.     

Tribological Properties of Phosphor Bronze and Nanocrystalline Nickel Coatings Under PAO + MoDTC and Ionic Liquid Lubricated Condition

The friction and wear properties of phosphor bronze and nanocrystalline nickel coatings were evaluated using a reciprocating ball-on-plates UMT-2MT sliding tester lubricated with ionic liquid and poly-alpha-olefin containing molybdenum dialkyl dithiocarbamate, respectively. The morphologies of the worn surfaces for the phosphor bronze and nanocrystalline nickel coatings were observed using a scanning electron microscope. The chemical states of several typical elements on the worn surfaces were examined by means of X-ray photoelectron spectroscopy. Results show that the phosphor bronze and nanocrystalline nickel coatings exhibited quite different tribological behaviors under different lubricants. Phosphor bronze plate shows higher friction coefficient (0.14) and wear rate (3.2 × 10⁻⁵ mm³/Nm) than nanocrystalline nickel coatings (average friction coefficient is 0.097, wear rate is 1.75 × 10⁻⁶ mm³/Nm) under poly-alpha-olefin containing molybdenum dialkyl dithiocarbamate lubricated conditions. The excellent tribological performance of nanocrystalline nickel coatings under above lubricant can be attributed to the formation of MoS₂ and MoO₃ on the sliding surface. a quite a number of C, O and F products on worn surface of phosphor bronze than NC nickel coatings can improve anti-wear properties while using ionic liquid as lubricant.     

Two-body abrasive wear of electroless nickel composite coatings

The two-body abrasive wear of electroless nickel (EN), EN-silicon carbide, and EN-alumina composite coatings have been investigated using a scratch test with a diamond indenter. The coatings were heat treated at temperatures of 100–500° C. The hardness of the coatings increased with heat treatment temperature from 500 HV100 for the as-deposited condition to 1008 HV100 when fully hardened. Scratch testing showed that the as-deposited coating had scratch tracks with a high degree of plasticity, signs of microploughing and tensile cracking and was characterised as a ductile failure. On the other hand, the heat-treated coatings showed chipping and cracking on the edge of the scratch tracks, failing in a brittle manner. The heat-treated EN-silicon carbide coatings, however, exhibited no cracking nor chipping, believed to be due to its higher fracture toughness than the other heat-treated coatings, attributable to its lower phosphorus content. The volume of material removed from the silicon carbide scratch track was 1/3 of the volume removed from the steel substrate at a 20 N load, and showed the best wear/ scratch resistance of any of the coatings tested.     

Sliding wear behaviour of Zinc–Nickel alloy electrodeposits

The sliding wear behaviour of zinc–nickel electrodeposited coatings on mild steel substrates was investigated using a spherical pin-on-disc apparatus. The pin materials were alumina and hardened steel. The composition of the coatings was the following: 86 wt% zinc–14 wt% nickel. The friction coefficient of zinc–nickel coating against alumina counter spheres was found to be higher than that against hardened steel counter spheres. The weight loss of zinc–nickel coating after sliding against hardened steel counter spheres was found to be lower than that against alumina counter spheres. The main wear mechanism of the zinc–nickel coating sliding against stainless steel was noted to be severe shearing of the surface layers of the coating due to the ploughing action of the steel pins. For the wear experiments of zinc–nickel coatings against alumina spheres, a surface delamination mechanism is proposed to be the predominant wear mechanism of the coatings.     

Wear behavior of electroless Ni–P–B4C composite coatings

In this research, the wear of electroless Ni–P and Ni–P–B₄C composite coatings was reviewed. Auto catalytic reduction of Ni in nickel sulfate and sodium hypophosphate bath including suspended B₄C particles with different concentration was used to create composite coatings with 12, 18, 25 and 33 vol.% of B₄C particles. Coatings 35 μm thick were heat treated at 400 °C for one hour in an argon atmosphere and the wear resistance and friction coefficient of heat-treated samples were determined by block-on-ring tests. All wear tests were carried out at 24 °C, 35% moisture, 0.164 m/s sliding speed and about 1000 m sliding distance. Graphs show that an electroless Ni–P–B₄C composite coating with 25 vol.% of B₄C had the best wear resistance against a CK45 steel counterface.     

Comparative study of the tribological properties of various modified mild steels under boundary lubrication condition

AISI1045 steel was modified by laser heat-treatment and conventional heat treatment. The friction and wear behaviors of the steel specimens after various surface modifications sliding against SAE52100 steel under the lubrication of liquid paraffin containing sulphurized olefin were comparatively investigated on an Optimol SRV oscillating friction and wear tester. The worn surface morphologies of the modified steel specimens were analyzed using a scanning electron microscope. The elemental compositions and chemical states of some typical elements on the worn surfaces of the modified steel specimens were analyzed with an energy dispersive X-ray analyzer and X-ray photoelectron spectroscope, respectively. It was found that the laser heat-treated specimen showed the highest hardness and best wear-resistance. The laser heat-treated and conventionally heat treated AISI1045 steel specimens sliding against SAE52100 steel under the lubrication of liquid paraffin containing sulphurized olefin registered smaller friction coefficients than under the lubrication of liquid paraffin alone. This was partly attributed to the increased hardness of the modified specimens. The tribochemical reaction between the steel and the active elements in the additive was involved in the sliding of the modified steel specimens against SAE52100 steel ball under the boundary lubricating condition, with the formation of a surface protective film composed of various tribochemical products. This also contributed to improve the friction and wear behavior of the modified steel specimens. The steel specimens subject to different surface modifications showed differences in the wear mechanisms under the boundary lubricating condition as well. Namely, the tempered steel specimen was mainly characterized by plastic deformation and pitting, the quenched specimen by grooves and delaminating, and the laser heat-treated one by polishing and mild adhesion.     

Transition of Mild Wear to Severe Wear in Oxidative Wear of H21 Steel

Under atmospheric conditions at 400 °C, we studied the wear mechanism of H21 steel with different tempering states as a function of normal load. Typical oxidative wear was identified by X-ray diffraction patterns with predominant tribo-oxides of Fe₃O₄ and Fe₂O₃. Under loads of 50–100 N, mild oxidative wear prevailed for all samples, such that the wear losses of H21 steel with various tempering states showed no significant differences with characteristics of a slight plastic deformation of the substrate and single-layer oxide. In this case, the wear rate was lower, and the tribo-oxide was decisive factor in determining wear rate. Under loads of 150–200 N, the transition of mild wear to severe wear occurred in H21 steel and was characterized by: (1) a significant difference of wear losses for steel with various tempering states; (2) wear loss that started to increase faster and reached a relatively high level; (3) the appearance of significant plastic deformation in the oxide underneath the substrate and multi-layer tribo-oxide. Under a load of 200 N for the steel tempered at 700 °C, plastic extrusion prevailed with a mixed metal-oxide layer.     

Sliding wear characteristics of gas boronized steel

The wear characteristics and the mechanism of sliding wear of boronized steel under unlubricated conditions were studied. Characteristic wear curves of FeB and Fe₂B boride layers formed on SAE 1045 steel were similar in form. The maximum wear rates were obtained under a sliding velocity of 0.30 m s^?1 for FeB specimens and 0.50 m s^?1 for Fe₂B specimens. Under such conditions both mechanical wear caused by scratching and oxidative wear occurred. Under conditions of mild wear the wear loss was caused mainly by oxidative wear. Under conditions of heavy wear destruction of the sliding surface was caused by thermal stress. The wear debris was composed principally of iron oxides (α Fe₂O₃, Fe₃O₄) formed by oxidative wear, α iron and borides (FeB, Fe₂B) produced by mechanical wear and B₂O₃ produced by the preferential oxidation of boron in the boride layer.     

The sliding wear of 316 stainless steel in air in the temperature range 20–500°C

The friction and reciprocating wear of 316 stainless steel in air has been investigated in the temperature range 20–500°C at constant load using a standard pin and flat geometry. A marked change in wear behaviour occurred above 300°C. From room temperature to 300°C the wear rate decreased slowly with increasing temperature. This was accompanied by an increasing fraction of oxide in the wear debris. At 300°C the debris consisted entirely of oxide with the α Fe₂ O₃ structure. In this temperature range wear can be explained essentially in terms of mild wear. Above 300°C the wear rate decreased by an order of magnitude and was accompanied by a severely distorted wear surface. There was a high proportion of metallic particles in the wear debris. The surface roughening occurs at an early stage of wear and stops when glazed oxide regions form. The low wear rate is explained in terms of the high hardness of the glazed load-bearing areas and re-incorporation of wear debris into the wear scar.     

Cutting forces,tool wear and surface finish in high speed diamond machining

We have investigated the cutting forces, the tool wear and the surface finish obtained in high speed diamond turning and milling of OFHC copper, brass CuZn39Pb3, aluminum AlMg5, and electroless nickel. In face turning experiments with constant material removal rate the cutting forces were recorded as a function of cutting speed between v_c = 150 m/min and 4500 m/min revealing a transition to adiabatic shearing which is supported by FEM simulations of the cutting process. Fly-cutting experiments carried out at low (v_c = 380 m/min) and at high cutting speed (v_c = 3800 m/min) showed that the rate of abrasive wear of the cutting edge is significantly higher at ordinary cutting speed than at high cutting speed in contrast to the experience made in conventional machining. Furthermore, it was found that the rate of chemically induced tool wear in diamond milling of steel is decreasing with decreasing tool engagement time per revolution. High speed diamond machining may also yield an improved surface roughness which was confirmed by comparing the step heights at grain boundaries obtained in diamond milling of OFHC copper and brass CuZn39Pb3 at low (v_c = 100 m/min) and high cutting speed (v_c = 2000 m/min). Thus, high speed diamond machining offers several advantages, let alone a major reduction of machining time.     

The effect of temperature on the unlubricated sliding wear of 5 CrNiMo steel against 40 MnB steel in the range 400–600°C

5 CrNiMo steel is used traditionally as hot forging die material in China. High temperature wear is a common failure mode of the steel. This paper deals with the sliding wear behavior of the steel in the temperature range 400°C to 600°C. The composition and features of the worn surface were analyzed using SEM, EDS and XRD. The oxidation of 5 CrNiMo steel under sliding wear condition at elevated temperature indicated that the oxide transfer layer formed on the sliding surface consisted of Fe₃O₄ and Fe₂O₃. The wear mechanism changed with the test temperature and the oxide transfer layer played an important part in the change in wear mechanism. At lower temperatures, wear was due to abrasive wear. From 500°C to 550°C, the oxide transfer layer presented a relatively compact morphology and the oxidational wear was the principal wear mechanism resulting in low wear rate at 500°C. When the test temperature was at 600°C, adhesive wear was predominant, and the wear rate increased greatly.     

Wear of aluminium bronze in sliding contact with lubricated stainless steel sheet material

Aluminium bronze, well known for its good sliding properties, is frequently applied as tool material in sheet metal forming (SMF) of stainless steel, e.g. for the production of washing, refrigeration and cooking equipment. The limited hardness of the material makes it, however, sensitive to tool wear that is: volumetric wear of the tool due to sliding contact with the sheet material. Conventional wear tests like the rubber wheel abrasion test or the Taber abrader test cannot be used to simulate the interaction of the tooling with lubricated sheet material. Dedicated tribo tests are therefore conducted with the slider-on-sheet test. The aim of the research is to measure the specific wear rate of aluminium bronze at SMF-like conditions. Experimental results showed a pronounced influence of lubricant selection and sheet material selection. The measured specific wear rate varied from 10⁻⁸ mm³/N m for a smooth stainless steel sheet quality to 10⁻⁶ mm³/N m for a rough surface quality.     

Performance of single crystal diamond tools with different rake angles during micro-grooving on electroless nickel plated die materials

In this study, experiments were carried out to establish the effect of tool rake angle on the performance of single crystal diamond tools in micro-grooving of electroless nickel plated molding dies. Diamond tools with rake angles of 0⁰,+5⁰ and ?5⁰ were used in the study, and it was found that the diamond tool with 0⁰ rake angle has superior performance in terms of tool wear, cutting forces, and machined surface roughness. For a cutting distance of up to 11.69 km, the 0⁰ rake tool machined satisfactorily without any sign of tool wear while the tools with +5⁰ and ?5⁰ rake angles suffered from progressive wear with a corresponding increase in cutting forces. However, it was noted that despite the increase in wear on tools with +5⁰ and ?5⁰ rake angles, and cutting forces on the diamond tools with all three different rake angles did not significantly affect the surface roughness. The effects of various cutting parameters such as spindle speed and infeed rate on the cutting forces and surface roughness are also presented in the study. It was observed that cutting forces increase proportionately with spindle speed and infeed rate without any significant variation of surface roughness. Surface quality of up to 3 nm Ra was achieved during micro-grooving of electroless nickel.     

Influence of solid lubricants and fibre reinforcement on wear behaviour of polyethersulphone

Polyethersulphone (PES), is an amorphous, brittle and high temperature engineering thermoplastic. Two composites of PES containing short glass fibres (GF) and solid lubricants viz. PTFE and MoS₂; and two composites containing short carbon fibre (CF) [30% and 40%] were selected for the present studies. Compositional analysis of selected materials was done with various techniques such as gravimetry, solvent extraction and thermal analysis viz. thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). These materials were studied for adhesive and abrasive wear performance by sliding against a mild steel disc and silicon carbide abrasive paper respectively, under different loads. It was observed that GF reinforcement along with incorporation of solid lubricants (PTFE and MoS₂) enhanced the wear performance of PES by an order of two. In the case of solid lubricants, PTFE proved to be more beneficial than MoS₂. CF reinforcement, however, proved to be the most effective in enhancing wear performance of PES. PES reinforced with 40% CF exhibited a specific wear rate in the order of 10⁻¹⁶m³/Nm which is considered to be very good for the thermoplastic composite. In the case of abrasive wear behaviour, however, incorporation of fibres or solid lubricants deteriorated the performance of the neat matrix. SEM was employed to investigate the wear mechanisms.     

Wear prevention in molds used to mold boron filled elastomers

An investigation was conducted to identify surface coatings which would improve the wear characteristics of compression molds used to mold contoured parts from elastomers filled with crystalline boron particles. An analysis was made of the mode of wear present on the surfaces of a production mold, followed by selection and modification of a capillary rheometer as the test device. Test specimens were coated by electroplating, electroless plating, plasma spraying, chemical vapor deposition, sputtering and a fused salt process. Testing was conducted under conditions simulating those encountered in the production molding operation.Techniques used in evaluating the results included optical microscopy, scanning electron microscopy, transmission electron microscopy and surface profilometry. The results are expressed as a ratio of volumetric wear of the tested coating to that of unprotected mold steel.Results indicate that titanium diboride (TiB₂) applied by chemical vapor deposition provides wear resistance superior to plasma sprayed aluminum oxide mixed with titanium dioxide, plasma sprayed chromium oxide, electrodeposited chromium, electroless nickel containing synthetic diamond powder, chemical vapor deposited tungsten carbide (W/W₂C), aluminum oxide and aluminum oxide over chromium carbide. Sputtered titanium diboride was also superior to these coatings and to sputtered titanium carbide and boron carbide.     

A comparative study on performance of multilayer coated and uncoated carbide inserts when turning AISI D2 steel under dry environment

The present work deals with a comparative study on flank wear, surface roughness, tool life, volume of chip removal and economical feasibility in turning high carbon high chromium AISI D2 steel with multilayer MTCVD coated [TiN/TiCN/Al₂O₃/TiN] and uncoated carbide inserts under dry cutting environment. Higher micro hardness of TiN coated carbide samples (1880 HV) compared to uncoated carbide (1430 HV) is observed and depicts better resistance against abrasion. The low erosion rate was observed in TiN coated insert compared to uncoated carbide. The tool life of TiN coated insert is found to be approximately 30 times higher than the uncoated carbide insert under similar cutting conditions and produced lower surface roughness compared to uncoated carbide insert. The dominant wear mechanism was found to be abrasion and progression of wear was steady using multilayer TiN coated carbide insert. The developed regression model shows high determination coefficient i.e. R² = 0.977 for flank wear and 0.94 for surface roughness and accurately explains the relationship between the responses and the independent variable. The machining cost per part for uncoated carbide insert is found to be 10.5 times higher than the multilayer TiN coated carbide inserts. This indicates 90.5% cost savings using multilayer TiN coated inserts by the adoption of a cutting speed of 200 m/min coupled with a tool feed rate of 0.21 mm/rev and depth of cut of 0.4 mm. Thus, TiN coated carbide tools are capable of reducing machining costs and performs better than uncoated carbide inserts in machining D2 steel.     

Friction and wear of carbon steel near T1-transition under dry sliding

The wear phenomenon of metals under dry sliding is, generally, divided into two modes of severe and mild wear. A discontinuous transition between the wear modes often takes place in a certain load range. The T₁-transition is usually observed at lower levels of load or sliding velocity. There is a great difference in wear rate between severe and mild wear. This indicates that the occurrence of severe wear should be avoided, especially in the field of machine design to prevent energy loss, occurrence of noise and vibration, and life reduction of machines and their components. Therefore, it is important for machine designers to know the relationship between friction and wear and the difference in properties of the wear surfaces in the two wear modes. In this study, wear tests of 0.35% C steel in contact with itself under constant load were conducted in moist air at various contact loads under dry sliding. The friction and wear were measured continuously throughout each test. After the tests, the relationship between friction and wear and the difference in properties of the wear surfaces were investigated in each wear mode. From the results, the upper and lower critical loads (P_acr and P_Acr) appeared between severe and mild wear. The phenomenon of zero wear has been newly found in the early period at very low loads. The zero wear continued for a long sliding distance and then changes to mild wear. The critical load between zero wear and mild wear is defined as P_zerowear. The load was changed once in a step-wise manner from low to high levels in process of test. Since the rubbing history under mild wear condition at the low load in the first stage affected the properties of wear surface, the wear mode at the high load in the second stage changed from ‘mild wear’ to ‘quasi-mild wear’ having a low rate. From the relationship between sliding distance necessary for the appearance of quasi-mild wear and contact load in the first stage, the boundary curve between severe wear and quasi-mild wear in the second stage is hyperbolic. This curve gradually approaches P_zerowear with decreasing contact load. Thus, P_zerowear is one of the important critical loads for elucidating the test results under varying load.     

Subsurface damage during dry sliding wear of Al-Al3Ni eutectic alloy

Cylindrical Al-Al₃Ni eutectic alloy wear pins (10 mm in diameter) were slid against a polished steel surface in a pin-on-disc rotating machine under unlubricated conditions with bearing pressures of 6–60 kPa and a constant sliding speed of 70 m min^?1. Metallographic changes in the subsurface region of contact were examined by optical microscopy and microhardness measurements. In the bearing pressure range investigated the alloy exhibited “mild” wear in two linear regions identified as pure “oxidative” wear at low bearing pressures and oxidative with superimposed “metallic” wear at higher bearing pressures. Plastic deformation and fragmentation of the Al₃Ni phase occurred under all bearing pressures. However, in composites prepared by unidirectional solidification containing large Al₃Ni particles fragmentation was insignificant. In all other specimens the size of the fragmented particles in the subsurface region of contact was about 5 μm irrespective of the bearing pressure.     

Fine friction cutting: a useful wear process

Friction cutting of metals was first reported almost 160 years ago. This review concentrates on its latest development, the slitting of nickel-chromium, titanium and ferrous alloys by toothless, water-cooled, mild steel discs spinning with a rim speed between 50 and 100 ms⁻¹. Slits an thin an 0.25 mm can be produced with little surface damage.Slitting occurs by adhesive wear. When oxidation leading to a mild wear state can be prevented, area slitting rates greater than 10 mm² s⁻¹ can be achieved: this is the case with nickel-chromium and titanium alloys and with soft or hardened stainless and tool steels. Oxidation cannot be prevented with carbon steels and most cast irons, so these metals cannot in general be slit usefully by fine friction cutting     

Tribochemical Wear of Rail Steels Lubricated with Synthetic Ester-Based Model Lubricants

Headchecks are a common type of damage in heavily loaded curved freight tracks. This paper deals with synthetic ester formulations' ability to prevent damage caused by headchecks through mild tribochemical wear. An experimental study pertaining to wear and friction of two rail steels lubricated by two synthetic ester base fluids, TMP-oleate and TMP-C₈-C₁₀, has been carried out. Six different free fatty acids were used in this study to act as performance additives. Three of the fatty acids were mono-acids with different, straight, carbon chain lengths (stearic acid C₁₈, decanoic acid C₁₀ and octanoic acid C₈), one was a mono-unsaturated straight-chain fatty acid (oleic acid C_18:1) while two were dibasic acids with intermediate carbon chain length (C₉ and C₁₀). Each fatty acid was blended with either ester, one at a time. The tests were carried out by using a high frequency reciprocating friction and wear test machine. In these tests, the gage face/wheel flange contact was simulated, and all tests were conducted in the boundary lubrication regime. An initial contact pressure of 316 MPa and a maximum sliding speed of 0.11 m/s were employed during the tests. The tests showed a wide range of wear rates, as well as different surface features depending on the interactions between synthetic esters, fatty acids and steel. The use of stearic and azaleic acid in lubricating rail steels results in very smooth surfaces with significant differences in their wear rates.