Rajnesh Tyagi

Tribological Properties of Laser Surface Texturing and Molybdenizing Duplex-Treated Ni-Base Alloy

Laser surface texturing (LST) and surface molybdenizing duplex-treatment was performed on Ni-base alloy in order to improve its wear resistance at high temperature. Surface molybdenizing was performed on the laser surface textured Ni-base alloy by a double glow plasma surface alloying technology. The friction and wear properties of the duplex-treated, the single-treated, and the untreated alloys were tested on a ball-on-disk tribometer by rubbing against an alumina ceramic ball from room temperature to 600°C. The topography of the laser surface textured dimples was measured by a white light interferometer and optical microscope. The dimples are 150-200 μ m in diameter and 45-50 μ m in depth. The distance between the dimples is 500 μ m. The molybdenized layer is approximately 20 μ m in thickness. The elastic modulus of Ni-base alloy is improved by molybdenizing. After texturing and the molybdenizing duplex treatment, the friction coefficient of the Ni-base alloy decreases from 0.38 to 0.26 at room temperature and from 0.42 to 0.34 at 600°C. The wear rate of the duplex-treated alloy is much lower than that of the pristine alloy at 600°C due to the textured dimples storing lubricious oxides.

Development of wear resistant medium carbon dual phase steels and their mechanical properties

Abstract Dual phase (DP) steels containing four different amounts of martensite ranging from 42 to 72 vol.-% have been developed from 0.42 wt-% carbon normalised steel by intercritical heat treatment at a fixed temperature of 740°C but varying holding times followed by water quenching. Mechanical properties of dual phase steels with increasing volume fraction of martensite have been investigated highlighting the effect of martensite content. The macrohardness has been found to increase with increasing martensite content in dual phase steel. The yield and tensile strengths have been found to increase with increasing amount of martensite whereas the percentage elongation and the percentage area reduction have been found to decrease. This has been attributed to the presence of hard and brittle martensite phase, which increases the strength at the expense of ductility. The mode of fracture has been found to change from purely ductile to mixed (ductile + brittle) as the martensite volume fraction increases from 42 to 72% in dual phase steels. Friction and wear properties under dry sliding conditions have also been found to improve with increasing martensite volume fraction in dual phase steels. The applications of medium carbon DP steels in the field of mineral processing and mining have been discussed.

Compositions and tribological properties of PEO coatings on Ti6Al4V alloy

ABSTRACT Hard oxide coatings were deposited on Ti6Al4V alloy using plasma electrolytic oxidation process from mixed aluminate/phosphate electrolytes. The influence of aluminate/phosphate proportion on the phase compositions, mechanical and tribological properties was systematically investigated. The results showed that plasma electrolytic oxidation (PEO) coatings with high compactness and hardness were formed in high aluminate/phosphate ratio electrolyte and the wear resistance and load bearing capacity were greatly improved due to the presence of hard γ- and α-Al2O3 phases. Low aluminate/phosphate ratio electrolyte led to thin and loose coatings without α-Al2O3 phase. It was shown that a thicker coating could provide only a limited improvement in wear resistance unless it is hard and free of porosity.

Tribological behaviour of titanium alloy modified by carbon–DLC composite film

Diamond-like carbon (DLC) films were deposited on both the untreated and the prior carbon ion implanted Ti6Al4V alloys by plasma enhanced chemical vapour deposition (PECVD). The tribological behaviours were evaluated by conducting reciprocating wear tests against ZrO2 using a ball on disc tribotester. The effect of ion implantation dose and zone on mechanical and tribological behaviour of DLC films was studied by means of nanohardness and nanoscratch tester, SEM and three-dimensional surface profiler. The duplex treatment dramatically increased the surface hardness and bonding strength of film/substrate. Both carbon ion implantation and PECVD improved the wear resistance of titanium alloy, whereas the combined process of carbon ion implantation with the dose of 1016 ions cm−2 and PECVD offered the best wear resistance by a reduction of 94·3% in wear volume in comparison to untreated alloy. The cracks and deformations that induced local flaking failure under high contact stress played an important role in the wear and failure mechanisms.

Modelling of dry sliding oxidation-modified wear in two phase materials

Abstract Models for oxidation-modified wear in two phase materials have been proposed extending the earlier models of Archard and Quinn, for predicting the oxidative wear in homogeneous materials. Three distinct possibilities have been considered—(a) case A, both the phases having the same oxidation behaviour and also, the same critical thickness for oxidative wear; (b) case B, both the phases having the same oxidation behaviour but distinctly different critical thicknesses; and (c) case C, both the phases having different oxidation behaviour and also, different critical thicknesses. In all these cases the wear rate varies linearly with the real area of contact estimated as the ratio of normal load to the rule of mixture hardness. The oxidation-modified wear in dual phase steels, as observed experimentally appear to belong to case A but it may also belong to case B with small difference in critical thickness in both the phases of ferrite and martensite. The wear behaviour calculated for case B is similar to those observed experimentally but the calculated values of wear rates are lower. It is possible that the oxidation behaviour could also be different in different phases and case C could be more appropriate.

Tribological behavior of Al-based self-lubricating composites

Abstract Aluminum-based composites containing either SiC (Al10%SiC) as the hard phase or a combination of SiC and MoS2 (Al10%SiC4%MoS2) have been synthesized following stir casting route. To overcome the poor wetting characteristics, magnesium was added in one of the composites (Al10%SiC4%MoS24%Mg) to improve the bonding between matrix and second phase. The results suggested an enhancement in hardness and strength of the composite containing SiC–MoS2 and Mg, thus indicating the effectiveness of Mg addition in improving the interfacial bonding strength. Tribological performance of the composites has been examined by carrying out pin-on-disk wear tests under dry sliding conditions at different normal loads of 9.8, 14.7, 19.6, and 24.5 N and at a constant sliding speed of 1 m/s. Both the friction coefficient and the wear rate have been found to reduce with addition of MoS2; however, bonding between the matrix and reinforcements was not good. Al10%SiC4%MoS24%Mg has shown the best tribological performance at all the loads in terms of the lowest friction coefficient and the lowest wear rate. The wear mechanism has been found to be a combination of adhesion and abrasion as indicated by the presence of some abrasive grooves and delaminated flakes at the worn surface and the X-ray examination of wear debris for all the materials used in the present investigation.

Biomechanical Analysis of Two-level Cervical Disc Replacement With a Stand-alone U-shaped Disc Implant

Study Design. Biomechanical study using a three-dimensional nonlinear finite element model. Objective. To analyze biomechanical changes with three prostheses based on two-level arthroplasty and to verify the biomechanical efficiency of dynamic cervical implants (DCIs) with a stand-alone U-shaped structure. Summary of Background Data. Few studies have compared biomechanical behavior of various prostheses as they relate with clinical results after two-level total disc replacement. Methods. Three arthroplasty devices Mobi-C, porous coated motion (PCM), and DCI were inserted at the C4–C6 disc space and analyzed. Displacement loading was applied to the center of the endplate at the C3 level to simulate flexion and extension motions. Results. The motion distributions in extension with DCI and in flexion with DCI and Mobi-C were relatively close to that in the intact model. Mobi-C and PCM obviously increased the combined extension range of motion at the index levels, but both resulted in about 45% decrease in extension moment. DCI showed a trend in strain energy similar to that of healthy discs. PCM exhibited a facet joint stress distribution almost similar to that of the intact model. DCI did not generate significant overloading at cartilage between the index levels, whereas the maximum facet joint stress increased with Mobi-C was about 39%. The maximum stress on a ultrahigh molecular-weight-polyethylene core was above the yield stress (42.43 MPa for Mobi-C and 30.94 MPa for PCM). Conclusion. Each prosthesis shows its biomechanical advantages and disadvantages. However, DCI has the capacity to preserve motion and store energy under external loading, similar to the behavior of normal discs. Compared with Mobi-C, both DCI and PCM showed a lower stress at cartilage between index levels, which may avoid facet joint degeneration to some extent. Such a well-controlled arthroplasty device with a stand-alone structure may be a potential candidate and needs to be investigated in future studies. Level of Evidence: 5

Dry sliding wear characteristics of in situ synthesized Al-TiC composites

Abstract Aluminum-based composites containing 0.06, 0.09, 0.12 fractions of in situ-synthesized TiC (Titanium carbide) particles have been prepared through in-melt reaction from Ai–SiC–Ti system following a simple and cost-effective stir-casting route. The TiC forms by the reaction of Ti with carbon which is released by SiC at temperatures greater than 1073 K. However, some amount of titanium aluminide (Al3Ti) is also formed. The formation of TiC has been confirmed through X-ray diffraction studies of the composite. The hardness and tensile strength have been found to increase with increasing amount of TiC. The friction and wear characteristics of the composites have been determined by carrying out dry sliding tests on pin-on-disc machine at different loads of 9.8 N, 19.6 N, 29.4 N, 39.2 N at a constant sliding speed of the 1 m/s speed. The wear rate i.e. volume loss per unit sliding distance has been found to increase linearly with increasing load following Archard’s law. However, both the wear rate and friction coefficient have been observed to decrease with increasing amount of TiC in the composite. This has been attributed to (i) a relatively higher hardness of composites containing relatively higher amount of TiC resulting in a relatively lower real area of contact and (ii) the formation of a well-compacted mechanically mixed layer of compacted wear debris on the worn surface which might have inhibited metal–metal contact and resulted in a lower wear rate as well as friction coefficient.

Development of Tribological Test Equipment and Measurement of Galling Resistance of Various Grades of Stainless Steel

A mechanized galling tester has been developed to evaluate the galling resistance of material pairs at room temperature (RT) as well as at elevated temperature condition. The test rig has a facility for online measurement of frictional torque during the test which is useful in assessing the incipient scoring. Both the test rig and the test method conform to the recent ASTM G196-08 standard. Galling resistance of two different grades of stainless steel SS 304 and 304 L has been evaluated in self-mated condition at RT and elevated temperature (300 °C). The parameter called galling50 has been reported for the materials tested. The galled surface indicated the severe plastic deformation in the direction of sliding and it is dominated by the typical adhesive wear mechanism. The recent ASTM G196-08 test method for measurement of galling resistance of material pairs appears to be superior to an older ASTM G98 because galling behavior was prevailed by the stochastic wear phenomenon.

Effect of Reinforcement Content and Technological Parameters on the Properties of Cu-4 wt.% Ni-TiC Composites

The present study deals with the synthesis and investigation of microstructure, density, and hardness behavior of Cu-4 wt.% Ni-TiC metal matrix composites, produced by high-energy ball milling, followed by compaction and sintering. Matrix of Cu-4 wt.% Ni was used, and different weight percentages (0, 2, 4, 6, and 8) of TiC particles were added. The uniform distribution of TiC particles in the matrix alloy was confirmed by characterizing these composite powders by using scanning electron microscope, energy-dispersive spectroscopy, and x-ray diffraction. Both the density and the hardness of the composite containing 4 wt.% TiC were found to be the highest. The density was found to decrease with increasing TiC content beyond 4 wt.%, and it has been attributed to the agglomeration of TiC particles leading to the formation of pores when added in relatively larger amounts. The compressibility behaviors of the milled powders were studied by using Panelli and Ambrosio Filho equation.