Effect of SiC addition on mechanical and wear characteristics of WC-32(W-Ti)C-6Co cemented carbides

The effect of silicon carbide (SiC) addition on mechanical and wear properties of cemented carbides was investigated in this study. Different percentages (1-7 wt.%) of SiC were added to the cemented carbides mixture of WC/32 wt. % (Ti-W) C/6 wt.% Co. The microstructural characteristics of the developed materials was identified using scanning electron microscopy (SEM) and Rockwell-A macrohardness (HRA), Vickers microhardness (Hv) as well as transverse rupture strength (TRS) were measured. The experimental results revealed that inserting SiC inclusion into the cemented carbides is found to be useless for two reasons. First, the microstructure of the developed carbides has more aggregations of largely contiguous SiC grains led to presence of rich/poor regions and consequently poor compatibility between carbides and the binder. Second, all properties of the cemented carbides greatly declined with the addition of SiC particles

The effects of material formulation and manufacturing process on mechanical and thermal properties of epoxy/clay nanocomposites

A holistic study was conducted to investigate the combined effect of three different pre-mixing processes, namely mechanical mixing, ultrasonication and centrifugation, on mechanical and thermal properties of epoxy/clay nanocomposites reinforced with different platelet-like montmorillonite (MMT) clays (Cloisite Na+, Cloisite 10A, Cloisite 15 or Cloisite 93A) at clay contents of 3–10 wt%. Furthermore, the effect of combined pre-mixing processes and material formulation on clay dispersion and corresponding material properties of resulting composites was investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), flexural and Charpy impact tests, Rockwell hardness tests and differential scanning calorimetry (DSC). A high level of clay agglomeration and partially intercalated/exfoliated clay structures were observed regardless of clay type and content. Epoxy/clay nanocomposites demonstrate an overall noticeable improvement of up to 10 % in the glass transition temperature (Tg) compared to that of neat epoxy, which is interpreted by the inclusion of MMT clays acting as rigid fillers to restrict the chain mobility of epoxy matrices. The impact strength of epoxy/clay nanocomposites was also found to increase by up to 24 % with the addition of 3 wt% Cloisite Na+ clays. However, their flexural strength and hardness diminished when compared to those of neat epoxy, arising from several effects including clay agglomeration, widely distributed microvoids and microcracks as well as weak interfacial bonding between clay particles and epoxy matrices, as confirmed from TEM and SEM results. Overall, it is suggested that an improved technique should be used for the combination of pre-mixing processes in order to achieve the optimal manufacturing condition of uniform clay dispersion and minimal void contents

Morphological structures and tribological performance of unsaturated polyester based untreated/silane-treated halloysite nanotubes

In this study, pristine halloysite nanotubes (HNT) and silane-treated halloysite (s-HNT) particles were incorporated into highly crosslink unsaturated polyester (UPE) to explore the morphological structure and tribological performance of UPE-HNT nanocomposite. Wear resistance of cured UPE/HNT and UPE/s-HNT nanocomposites were systematically evaluated using block-on-ring (BOR) configuration against stainless steel counterpart under a certain dry sliding conditions. TEM micrographs revealed a uniform morphological dispersion of halloysite particles in the UPE matrix. Both pristine and silane-treated HNT particles induced a modest decrease in a specific wear rate and coefficient of friction of nanocomposites. There was a pronounced reduction in the specific wear rate of the polyester composites at more than 5 wt.% of halloysite. However, the addition of silane exhibited insignificant results especially at higher percentages of HNT. The investigation of worn surface morphology and wear mechanism of materials by using SEM is also discussed

Role of silanized halloysite nanotubes on structural, mechanical properties and fracture toughness of thermoset nanocomposites

This study investigates the structure/property relationship of thermosetting unsaturated polyester (UPE)filled with pristine halloysite (HNT) and vinyltrimethoxysilane-treated halloysite nanotubes (s-HNT)nanocomposites. The dispersion of particles and morphological structures of the nanocomposites were examined using TEM and XRD analysis as well as Fourier Transform Infrared spectroscopy (FTIR). Thermogravimetric analysis (TGA) and mechanical properties were characterized. The evaluation of stress intensity factor (KIc) was measured based on linear elastic fracture mechanics (LEFM) and single-edge notch bending (SENB) geometry to identify the role of silanized halloysites on toughening improvement. It was found that modifying UPE matrix with HNT or s-HNT changed the crystalline structure of the UPE nanocomposites, indicating a high degree of halloysite orientation. Uniform dispersed halloysites are observed in the s-HNT/UPE versus skewed-like clusters in the HNT/UPE nanocomposite. The introduction of HNT or s-HNT up to 5 wt.% induced higher mechanical properties and improved fracture toughness associated with a shift in toughening mechanisms from a highly brittle fracture for neat UPE into matrix shear yielding and zone shielding mechanisms with the presence of halloysite particles in the nanocomposite

Toughening of brittle polyester with functionalized halloysite nanocomposites

This study presents the role of pristine halloysite nanotubes (HNT) and silane-functionalized halloysite (s-HNT) on toughening mechanisms and initiating plastic deformation in unsaturated polyester (UPE) nanocomposite. The critical stress intensity factor (KIc) and the critical strain energy release rate (GIc) as fracture toughness indications were measured and the relationship between the morphological structures and toughening mechanisms was identified. The results indicated that the fracture toughness values exhibited a steady-state increasing trend with the incorporation of up to 5 wt % HNT or s-HNT into the UPE resin. The 3% HNT or 3% s-HNT composites were found to obtain the highest toughness values supported with uniformly dispersed particles. The SEM observations showed different energy dissipation mechanisms are; zone shielding and shear yielding with a presence of full particle debonding with the HNT addition; and river line patterns, a tail-like structure and the formation of micro-cracks mechanisms were observed with the addition of s-HNT

Effect of compacting pressure on microstructure and mechanical properties of carbide cutting tools

The effects of compaction pressure on properties of carbide cutting tools containing 80·5 wt-%WC, 5 wt-%TiC, 5 wt-%TaC–NbC and 9·5 wt-%Co were studied. These tools were formed by powder metallurgy with different compacting pressures ranging from 77 to 231 MPa (5–15 tons in-2) and sintered in a vacuum furnace at a constant sintering temperature (1450°C) and at a constant heating and cooling rate of 5°C min-1. Green and bulk densities, shrinkage and hardness of the produced compacts were measured. Tool cutting performance has been assessed based on machining a medium alloyed steel workpiece under different cutting conditions and measuring the tool flank wear and the workpiece surface roughness. The microstructure of the compacts was metallographically examined using scanning electron microscopy. The results have revealed that both densities and hardness figures increase with increasing compaction pressures, while shrinkage decreases. Cutting performance has not demonstrated a substantial improvement of the tool’s performance and life due to the increasing compacting pressure of these tools

Impact fracture behaviour of silane-treated halloysite nanotubes-reinforced unsaturated polyester

This work investigates the effects of untreated and silane-treated halloysite nanotube (HNT) particles on the micromechanism of plastic deformation of unsaturated polyester (UP) nanocomposites under impact loading conditions. The impact fracture properties of the prepared materials were characterised based on the temperature range of -20 to +60 °C using falling weight impact tester. The chemically-modified halloysite with silane coupling agent (s-HNT) showed less hydrophilic towards the polyester matrix, thereby a good interfacial adhesion and uniform structures of HNT in the matrix are obtained compared to the untreated. The incorporation of both unmodified and modified HNT particles up to 5 wt.% into the UP revealed a modest increase in the impact strength and total energy of nanocomposites, since the well dispersed particles in the matrix hindered the crack propagation under the impact loading. SEM examinations revealed that the fracture mode on UP surface was a smooth fast brittle while, the nanocomposite surfaces showed a sign of plastic deformation

The synergistic effect of hybrid flame retardants on pyrolysis behaviour of hybrid composite materials

The aim of this investigation is to comprehensively understand the polymeric composite behavior under direct fire sources. The synergistic effects of hybrid flame retardant material on inhabiting the pyrolysis of hybrid reinforced fibers, woven roving (0°- 45°) carbon and kevlar (50/50 wt/wt), and an araldite resin composites were studied. The composites were synthesised and coated primarily by zinc borate (2ZnO.3B2O3.3.5H2O) and modified by antimony trioxide (Sb2O3) with different amounts (10 - 30 wt %) of flame retardant materials. In the experiments, the composite samples were exposed to a direct flame source generated by oxyacetylene flame (~3000 ºC) at variable exposure distances of 10 - 20 mm. The synergic flame retardants role of antimony trioxide and zinc borate on the composite surface noticeably improves the flame resistance of the composite which is attributed to forming a protective mass and heat barrier on the composite surface and increasing the melt viscosity