S. Balasivanandha Prabu

Comparison of TiAlN, AlCrN, and AlCrN/TiAlN coatings for cutting-tool applications

Monolayer and bilayer coatings of TiAlN, AlCrN, and AlCrN/TiAlN were deposited onto tungsten carbide inserts using the plasma enhanced physical vapor deposition process. The microstructures of the coatings were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM micrographs revealed that the AlCrN and AlCrN/TiAlN coatings were uniform and highly dense and contained only a limited number of microvoids. The TiAlN coating was non-uniform and highly porous and contained more micro droplets. The hardness and scratch resistance of the specimens were measured using a nanoindentation tester and scratch tester, respectively. Different phases formed in the coatings were analyzed by X-ray diffraction (XRD). The AlCrN/TiAlN coating exhibited a higher hardness (32.75 GPa), a higher Young’s modulus (561.97 GPa), and superior scratch resistance (LCN = 46 N) compared to conventional coatings such as TiAlN, AlCrN, and TiN.

Metallurgical Characteristics of TiAlN/AlCrN Coating Synthesized by the PVD Process on a Cutting Insert

TiAlN/AlCrN coating was deposited on a tungsten carbide insert, using the plasma-enhanced physical vapor deposition (PEPVD) process. The microstructure of the coating was examined and it was found that the TiAlN/AlCrN coating was uniform, highly dense, and less porous. The different phases formed in the coating were analyzed using the x-ray diffraction. The hardness and scratch resistance were measured using the nanoindentation tester and scratch tester, respectively. TiAlN/AlCrN exhibited higher hardness, higher Young’s modulus, and superior scratch resistance when compared to the conventional coatings, such as TiAlN, AlCrN, and TiN. The surface morphology of the coating was characterized using the atomic force microscope (AFM). The surface roughness was found to be lesser in the TiAlN/AlCrN coating. The TiAlN/AlCrN coating has proved to have better corrosion resistance, compared to the uncoated carbide substrate.

Influence of Processing Temperatures on Mechanical Properties and Microstructure of Squeeze Cast Aluminum Alloy Composites

The paper deals with the influence of melt and die temperatures on the squeeze cast silicon carbide particulate reinforced aluminum alloy composites. Samples were produced at the following constant melt and die temperatures: melt—750, 800, 850, and 900°C; die—250, 300, 350, and 400°C. During the specimen fabrication, pressure was maintained at 100 MPa. The results reveal significant influence of both melt and die temperatures on the mechanical properties. The optimum melt and die temperatures for the preparation of the composite are 850°C and 350 °C, respectively. Tensile and impact strengths, and hardness of composite samples prepared at this temperature combination are found to be better than those of samples prepared at other temperatures. Additionally, microstructures of samples prepared at this temperature combination display a relatively fine grain structure and the smallest degree of particle agglomeration which explain the dependence of mechanical properties on the melt and die temperatures.

Interfacial Thermal Resistance and the Solidification Behavior of the Al/SiCp Composites

The objective of this investigation is to study the effects of applied pressure on the solidification time and interfacial thermal resistance of A356/10% SiCp during squeeze casting. Samples were prepared for various but constant squeeze pressures up to 130 MPa while maintaining the melt and mold temperatures at 800°C and 400°C, respectively. It was observed that the solidification time was 60 s when no squeeze pressure was applied but it decreased to 42 s when the squeeze pressure was maintained at 130 MPa. The results also showed that the cooling rate increased with squeeze pressure. The solidification time calculated from one-dimensional heat flow theory was found to be close to that obtained from the experimental cooling curves. The interfacial thermal resistance between the mold and the casting was calculated and it decreases when the squeeze pressure increases.

Finite element based investigation on vibrational performance of a sandwich system

This work aims at estimating and comparing the frequency and loss factor of a mild steel sandwich shaft disc system containing viscoelastic, electro-rheological fluid (ERF), and magneto-rheological fluid (MRF) core materials with mild steel as the facing layers. Because the structure is axisymmetric, a semi-analytical finite element method was implemented to study the frequency and loss factor values of the mild steel sandwich shaft disc system. The effects of an electric field for the ERF material and a magnetic field for the MRF material on the vibration behavior of the mild steel sandwich shaft disc system were studied. A quantitative study identified the combination of mild steel facing with a viscoelastic core shaft disc system that produced the highest frequency and loss factor values. In addition, the effect of an electric field and a magnetic field on ERF and MRF core improves the damping performance of the structure.

On the role of process parameters of aluminothermic reaction synthesis of in-situ Al -TiB2 composites: microstructure and mechanical properties

This is an account of a process that has led to an application for a patent of relevance to the metal cutting industry and the paper examines the scientific aspects like the influence of process parameters of aluminothermic reaction synthesis of in-situ Al-TiB 2 metal matrix composites on their microstructure and mechanical properties. The reaction between the salts potassium fluoborate (KBF 4 ) and Potassium hexafluorotitanite (K 2 TiF 6 ) in the aluminium melt leads to the formation of TiB 2 particles. The process parameters of reaction time (Rh), reaction temperature (Rt) and weight percentage of precursors (W) were carefully controlled in order to regulate the volume fraction of TiB 2 formation in the aluminium melt. Detailed microstructure analysis at different processing conditions revealed that particle clustering was present in the reinforcement and that this changes the hardness and density of the resultant composites. Addition of cryolite, which is a surface-active salt, prevented agglomeration and emulsification at high temperatures and also facilitated the uniform distribution of the particles in the matrix. The prepared Al-TiB 2 composites were tested for their tensile properties, density and hardness. Both hardness and yield strength are found to increase with an increase in the percentage of reinforcement. The percentage elongation decreases due to an increase in TiB 2 ceramic particle content in the matrix. It is found that the reaction time plays a major role in TiB 2 growth and the distribution of TiB 2 particles within the matrix.

Deformation behaviour and failure mechanisms of Al–TiB2 in situ composites

Abstract The deformation behaviour and failure mechanisms of Al–TiB2 in situ metal matrix composites were examined through uniaxial tension and compression tests. The influence of particle size and holding time was found to have stronger influence. Elastic modulus of the composite during tension and compression was higher than that of the unreinforced matrix. Fractographic morphology studies were done using optical and scanning electron microscopy. Results reveal that the primary failure was due to matrix yielding initiated by the slip lines. A dimpled structure of the matrix is observed indicating that the failure occurred by microvoid coalescence. The specimens also exhibit plastic microbuckling phenomena at the circumference, followed by particle fracture adding up to the failure mechanisms during compression. Compressive strength and tensile elastic modulus were very sensitive to change in the percentage reinforcement. During compression, majority of the samples failed by splitting or splaying mode. In tension, the particles influence the failure mechanism, whereas in compression they act as barriers to the matrix flow.

Effect of the squeeze pressure on the mechanical properties of the squeeze cast Al/SiCp Metal Matrix Composite

This paper presents the results of a study carried out to understand the effect of the squeeze pressure on the mechanical properties of Al/SiCp composites, fabricated by the squeeze casting technique. Aluminium (A356) alloy reinforced with SiC particles were prepared using the stir casting route. The SiC particles are distributed in the liquid Al alloy matrix by mechanical stirring, and the melt is then subjected to different squeeze pressure during solidification. Microstructure examination of the squeeze cast composites showed the SiC particle distribution and the grain refinement in the Al alloy matrix due to the applied pressure. The hardness and density distribution also carried out to correlate with the particle distribution. The tensile and impact strength value linearly increase with the applied squeeze pressure due to the uniform distribution of particle and effect of grain refinement. At 100 MPa, the sound cast Al/SiCp composites are produced with superior hardness and tensile properties.

Synthesis and characterisation of nanocrystalline hydroxyapatite from sea shells

Nanocrystalline hydroxyapatite was synthesised by wet chemical reaction between sea shells (CaCO3) which were thermally converted to amorphous calcium oxide (CaO) and then to calcium hydroxide (Ca(OH)2) and reacted with phosphoric acid (H3PO4). Two experiments were conducted using wet chemical synthesis method. Hydroxyapatite (HA) was synthesised by slow addition of phosphoric acid in to calcium hydroxide (Ca(OH)2) without microwave irradiation and in another method; microwave irradiation was carried out after the reactants were combined in a similar manner. In both the experiments, the Ca:P ratio of 1.67 was maintained. pH of the solution was maintained at 9 to avoid the formation of calcium deficient apatites. The synthesised samples show XRD patterns corresponding to hydroxyapatite. The wet chemical process without microwave irradiation resulted in rod shaped HA particles of size 101 nm, whereas microwave irradiation of the solution after reaction also resulted in rod shaped HA but the particle size was only 68 nm as evidenced from XRD analyses. The TEM analyses reveal average aspect ratios of 3.37 ± 1.28 and 5.98 ± 2.28 for methods without and with microwave irradiation respectively.

Comparative Evaluation of Performances of TiAlN-, AlCrN- and AlCrN/TiAlN-Coated Carbide Cutting Tools and Uncoated Carbide Cutting Tools on Turning EN24 Alloy Steel

In the present work, the performances of TiAlN-, AlCrN- and AlCrN/TiAlN-coated and uncoated tungsten carbide cutting tool inserts are evaluated from the turning studies conducted on EN24 alloy steel workpiece. The output parameters such as cutting forces, surface roughness and tool wear for TiAlN-, AlCrN- and AlCrN/TiAlN-coated carbide cutting tools are compared with uncoated carbide cutting tools (K10). The design of experiment based on Taguchi’s approach is used to obtain the best turning parameters, namely cutting speed (V), feed rate (f) and depth of cut (d), in order to have a better surface finish and minimum tool flank wear. An orthogonal array (L9) was used to conduct the experiments. The results show that the AlCrN/TiAlN-coated cutting tool provided a much better surface finish and minimum tool flank wear. The minimum tool flank wear and minimum surface roughness were obtained using AlCrN/TiAlN-coated tools, when V=160m/min, f=0.318mm/rev and d=0.3mm.