Investigating the performance of TiN and TiAIN coatings on milling cutter used for machining bimetal steel strip

Surface engineering of cutting tools (single point or multipoint) through advanced coatings (e.g., TiN) has contributed towards considerable improvement of tool life, productivity and machining quality [1] by modifying the tool substrate. New coating species (e.g., TiAlN) are also being developed to further improve the performance of cutting tools. In this study, milling tests were carried out with a TiN and TiAlN coated milling cutter to compare their performance. Physical Vapour Deposition (PVD) technique was used to deposit the coatings after carefully preparing the cutting edges. Flank wear measurement in the milling cutter teeth was used as the criterion for assessing performance of the coatings. It has been found that TiAlN coating has significantly reduced the flank wear in the milling cutter teeth compared to TiN coating both at new and reground conditions of the cutter. Abrasive and adhesive wear were identified as the main mechanisms of the flank wear in both TiAlN and TiN coated teeth. The information should be useful for tool designers, coating suppliers and manufacturing engineers

Deposition of hard and solid lubricant (TiN + MoSx) coating by closed-field magnetron sputtering; Julfikar Haider

Vapor deposited thin coatings have served well as mechanically hard coatings in different practical applications e.g., cutting and forming tool industries, decorative industries, biomedical industries etc. Some of these coatings (i.e., TiN) have a high coefficient of friction and can cause abrasion and rapid wear of the opposing surface. In a closed-system, a hard coating constitutes a source of abrasive particles upon spallation within the mechanism, which can lead to a worse result than the uncoated surface. Increasing number of reports in literature has suggested the use of a hard solid lubricant based coating to avoid this problem. A sputtering rig was made operative as a closed-field magnetron sputtering system by reestablishing different systems (magnetron, water cooling, vacuum, electrical etc.). A heavy-duty impact-abrasion wear tester was modified for applying lower load on the coated sample during abrasion by a spring-loaded mechanism. A single-axis and double-axis rotary substrate table system was designed, manufactured and successfully installed in the existing sputtering system. This substrate table facilitated the rig for the deposition of multicomponent and multilayer composite coating by using different target materials and reactive gases. A rotational control mechanism has been developed to rotate the substrate table at slower speed in front of activated targets and faster speed in front of inactivated targets within a single rotation instead of rotating at constant speed. This system increased the deposition rate thus saving time and materials. A three dimensional Computational Fluid Dynamics (CFD) study has been carried out using FLOTRAN-CFD code of the ANSYS analysis package to predict the velocity, pressure and concentration distribution of the process gas species (argon and nitrogen) across the sputtering chamber, inlets and outlet. The numerical predictions provided useful understanding of the multiple species process gas distribution and their mixing behaviour at various gas flow rates to some extent. Modelling of thermal stress developed during cooling of a typical coating-substrate system (TiNstainless steel) from deposition to room temperature was performed using the finite element code ANSYS. A parametric study was performed to analyse the effects of coating and substrate thickness, Young’s modulus, deposition temperature etc. on the thermal stress. Radial, tangential, axial and shear stress distribution through the thickness of the coating and substrate were examined. The interface of the coating and substrate was recognised as the critical location from the failure point of view. Ti interlayer between TiN coating and substrate has significant influence on the reduction of thermal stress at the interface. The deposition of composite hard and solid lubricant coatings (TiN+MoSx) has been performed on a rotating substrate by closed-field magnetron sputtering using separate Ti and MoS2 targets in a nitrogen gas environment. The composition of the coating was varied by controlling target current, gas pressure, and target to substrate distance. Compositional and structural analysis indicated the presence coating species (Ti, N, Mo and S) and incorporation of Mo and S atoms in the TiN matrix. The change of process parameters during deposition was also reflected in the measurements. For instance with the increase of MoS2 target current, higher peak shifting and peak widening were observed in XRD study. The TiN+MoSx coating showed slightly lower hardness than pure TiN coating but higher hardness than MoSx coating. The hardness could not be directly correlated with the tribological properties. The adhesion test for all TiN+MoSx coatings showed a better adhesion compared to pure TiN and MoSx coatings. The TiN+MoSx coating also showed lower coefficients of friction than TiN in Pin-on-disk wear tests possibly due to the solid lubrication effect from MoS2 formed during sliding. This fact was also speculated based on the results of the optical investigation of the wear track

Effect of Chemical Treatment on Thermal Properties of Jute Fiber Used in Polymer Composites

In recent years, natural fibers, such as jute has gained significant research interest in order to fabricate fiber reinforced polymer composites. Chemical treatments are generally carried out on the raw fibers for making composites with improved properties. From a composite manufacturing point of view, it is important to understand how the treatments can affect the thermal properties of the jute fiber. In the present research, the effects of rot-retardant, fire-retardant and water-retardant treatments on thermal properties of the jute fiber were investigated. Fiber samples were collected from the middle portion of whole jute fiber. Thermo-gravimetric analysis (TGA) and differential scanning calorimetric (DSC) analysis were subsequently conducted on the jute fiber for thermal characterization. The results demonstrated a lower thermal decomposition temperature in the case of fire-retardant treated jute fiber but higher residue at above 400 °C, as compared to the raw and other treated fibers. In general, it was found that chemically treated fibers absorbed less heat, in contrast to the raw jute fiber and heat flow became negative in all cases of the treated fibers. This study provides important information about the thermal properties of the treated jute fibers for manufacturing polymer-based composite materials

Effect of repeated firing on the topographical, optical, and mechanical properties of fully crystallized lithium silicate-based ceramics

Statement of problemThe influence of different firing protocols on the topographical, optical, and mechanical properties of fully crystallized computer-aided design and computer-aided manufacturing (CAD-CAM) lithium silicate-based glass-ceramics (LSCs) for dental restorations remains unclear.PurposeThe purpose of this in vitro study was to investigate the effect of different firing regimens on the surface roughness, gloss, Martens hardness, indentation modulus, biaxial flexural strength, and crystalline structure of fully crystallized CAD-CAM LSCs and the effect of their interposition on the irradiance of a light-polymerization unit.Material and methodsThree fully crystallized CAD-CAM LSC blocks were evaluated (N=150): lithium disilicate (Initial LiSi Blocks; LS), zirconia-reinforced silicate (Celtra Duo; CD), and lithium aluminum disilicate (CEREC Tessera; CT). Specimens were allocated to 5 subgroups according to their firing protocol. LSC roughness (Sa) was measured with an optical profilometer, and gloss (GU) was detected with a gloss meter. Martens hardness (HM) and indentation modulus (EIT) data were obtained from a hardness testing machine. The irradiance of a light-polymerization unit and transmittance of LSCs were measured with an instrument (Managing Accurate Resin Curing-Light Collector; BlueLight analytics, Inc) subsequent to ceramic interposition. Crystalline phases were analyzed by X-ray diffraction, and biaxial flexural strength (σ) was determined by the ball-on-3-ball method in a universal testing machine followed by Weibull analysis to calculate characteristic strength (σ0) and Weibull modulus (m). Two-way ANOVA and Tukey HSD post hoc tests (α=.05) were used to analyze the data.ResultsStatistically significant differences were found among different treatment groups based on Sa, GU, HM, and EIT values (P<.001). Delivered irradiance was significantly reduced following CT (P<.01) and glazed LSC (P<.005) interposition. CD displayed highest biaxial flexural strength and reliability after 1 firing cycle (σ=568.2 MPa, m=16.8) CONCLUSIONS: The type of material and firing regimens had a significant effect on the topographical, optical, and mechanical properties of fully crystallized CAD-CAM LSCs. Glazing significantly reduced delivered irradiance, Martens hardness, and biaxial flexural strength