P. Kesavan Nair

Studies on crystallization of electroless NiP deposits

Abstract Electroless Nickel-Phosphorus deposits with phosphorus content of 4.35, 5.45, 6.80, 8.10 and 9.12 Wt.% P were made, on mild steel substrates. The deposits were annealed at 60, 100, 200, 300, 330, 360, 400 and 600°C for 2 hours. The crystallization process of these deposits was studied using X-ray line profile analysis, differential scanning calorimetry and microhardness. The X-ray diffraction pattern of all the deposits indicated the presence of crystalline and amorphous phases coexisting in the as deposited condition. The lattice disorder in the crystalline phase increased with increasing phosphorus content. Profile refinement techniques have been used to separate the crystalline nickel (111) reflection from the amorphous profile. The separated (111) and (222) profiles of nickel were used for crystallite size and microstrain analysis. The crystallite size of nickel was found to vary from 50A in the as deposited condition to about 600A in the fully annealed state (400°C). The crystallite size increased sharply above 300°C, indicating the onset of precipitation. The microhardness values showed typical precipitation hardening type of behavior, increasing from an initial value of about 450 VHN in the as deposited state to the peak hardness of about 825 to 950 VHN, corresponding to a temperature range of 360 to 400°C. Differential scanning calorimetry of these deposits, indicated only one major reaction between 325 to 375°C. Ni 3 P has been identified as the final stable precipitate at 600°C.

A study on the wear resistance of electroless Ni–P/Diamond composite coatings

Abstract The ability to co-deposit particulate matter in a matrix of electroless nickel has led to a new generation of composite coatings. Polycrystalline diamond is one of the many varieties of particulate matter that can be co-deposited. Composite diamond coating is a regenerative layer of fine diamond particles dispersed in a hard electroless nickel matrix. In this work, experiments have been carried out to study the effect of heat treatment, particle size and phosphorus content on the wear characteristics of the composite electroless coating containing diamond particles. The results indicate substantial increase in wear resistance after the coated sample containing 9–10 wt.%. P content having fine diamond particle size is annealed around 350°C.

Competition between nucleation and early growth of ferrite from austenite—studies using cellular automaton simulations

Abstract A model for the nucleation of ferrite on austenite grain boundaries and the growth of these nuclei along the grain boundary and into the grain, is developed. A cellular automaton algorithm, with transformation rules based on this model, is used to simulate the decomposition of austenite into ferrite. When performed under continuous cooling conditions, the simulations give an insight into the competition between nucleation and early growth, which determines the variation of ferrite grain size with the cooling rate and with austenite grain size. The number of ferrite grains per austenite grain, ferrite grain size and the kinetics of ferrite formation are obtained as a function of the cooling rate and austenite grain size. Contour plots of the volume fraction of ferrite in the cells at different times, enables visualization of the ferrite growth process.

Performance of TiCN and TiAlN tools in machining hardened steel under dry, wet and minimum fluid application

In this work, an experimental study has been carried out on the comparative performance of TiCN and TiAlN coated tools in machining of AISI 4340 hardened steel under dry, wet and minimum fluid application conditions and the analysis of results are presented. Cutting force, cutting temperature, surface finish and flank wear are compared in all the cases to understand the performance. Then, the relative influences of the machining and the minimum fluid application parameters on the machining performance of tools have been analysed and presented in this paper.

Influence of cryogenic treatment on the wear characteristics of 100Cr6 bearing steel

A series of reciprocating wear tests were performed on the deep cryogenically treated and conventionally heat-treated samples of 100Cr6 bearing steel to study the wear resistance. The worn surfaces as well as the wear debris were analyzed by scanning electron microscopy. The improvement in wear resistance of the deep cryogenically treated samples ranges from 49% to 52%. This significant improvement in wear resistance can be attributed to finer carbide precipitation in the tempered martensitic matrix and the transformation of retained austenite into martensite. X-ray diffraction analysis shows that the volume fraction of retained austenite in the conventionally heat-treated samples is 14% and that of the deep cryogenically treated samples is only 3%.

Residual stresses of types II and III and their estimation

Residual stresses (RS) are induced in metallic materials by a variety of working and fabrication processes. They are generally classified into three categories (types I, II and III) depending upon their range of influence. Separation of type I and II stresses often requires stress measurements on thin specimens. Type III stresses are related closely to grain fragmentation and micro-strains associated with plastic deformation. Perhaps the oldest and the most rigorous method of estimating these stresses is still the Warren-Averbach analysis developed during the late forties/early fifties. Other techniques involving integral breadths and variance of the profiles have also been developed. In all these methods developed during the early stages, prior to seventies, a major requirement was well-separated non-overlapping profiles. The late sixties and early seventies saw a dramatic increase in computational capabilities with the advent of powerful electronic computers. This led to the introduction of curve-fitting procedures into the field of X-ray diffraction. The most remarkable achievement of this period is the development of the Rietveld Method. Although this method was initially developed to tackle the neutron diffraction profiles, which are as a rule nearly symmetric and Gaussian in nature, the method saw rapid developments during the eighties. At present, techniques based on concepts developed by Rietveld could be applied to essentially asymmetric and non-Gaussian multiple spectral components of X-ray diffraction profiles. Pattern decomposition techniques which separate composite powder diffraction profiles into individual profiles are now available. In combination with single line profile analysis techniques, this provides a powerful tool in the hands of researchers. A typical example of such a single line profile analysis is given.