Vickers Hardness Of Composites Research Articles

Effects of graphene content on the microstructure and mechanical properties of alumina-based composites

In this work, alumina-graphene (Al2O3-G) composites with graphene contents ranging from 0.5 to 3% were prepared by stepwise feeding ball milling and hot pressing. The influences of graphene content on the microstructure and mechanical properties of Al2O3-G composites were investigated. Results showed that the densification, grain sizes, flexural strength, fracture toughness and Vickers hardness of materials increased firstly and then decreased with increasing graphene contents. When the graphene content was 1%, the value of each performance parameter reached the maximum. The average grain size of material decreased from 991 to 551 nm as the graphene content increased from 0 to 1%, but it increased to 863 nm when the graphene content was 3%. The flexural strength, fracture toughness and Vickers hardness of composites with graphene content of 1% increased to 763.5 MPa, 7.4 MPa m1/2 and 21.28 GPa. Compared with the Al2O3, the fracture strength and toughness of the composites increased by up to 54.63 and 65.54%. Analysis suggested that the strength of Al2O3-G composites was mainly related to the grain size and preexisting microflaws.

Comparative investigation on microstructures and mechanical properties of (TiB + TiC)/Ti-6Al-4V composites from Ti-B4C-C and Ti-TiB2-TiC systems

Two percentages of TiB + TiC reinforced Ti-6Al-4V composites from Ti-B4C-C and Ti-TiB2-TiC systems were fabricated by reactive hot-pressed sintering. Their microstructures and mechanical properties involving elastic modulus, Vickers hardness, bending strength and wear property were investigated comparatively. The experimental results show that needle-like TiB whiskers and near-equiaxed TiC particles are evenly distributed in the Ti-6Al-4V matrix. The mechanical properties of the (TiB + TiC)/Ti-6Al-4V composites are closely related with the nominal composition and synthesis system of TiB + TiC reinforcement and the microstructures of composites. With increasing the nominal volume fraction of reinforcement, both elastic modulus and Vickers hardness increase more or less and the bending strength decreases in varying degrees. A certain increase of pores in the composites with the sintering temperature increasing to 1300 °C can markedly affect the bending strength. Moreover, no matter what the sintering temperature and nominal volume fraction of reinforcement, the elastic modulus and Vickers hardness of composites from the Ti-TiB2-TiC system are higher than those from the Ti-B4C-C system. Similarly, the composites from the Ti-B4C-C system present better abrasion resistance than those from the Ti-TiB2-TiC system due to the difference of interfacial bonding between the TiC particles and Ti-6Al-4V matrix in the two kinds of composites.

Effect of Nanocrystalline TiB2 Addition on Properties of Copper Powder Reinforced Epoxy Composites

The present investigation aims at understanding the influence of nanocrystalline TiB2 powder on thermal and mechanical properties of Epoxy–Cu microcomposites. The nanocrystalline TiB2 powder has been synthesized by SHS and the particle size is in the range of 60–70 nm as revealed from TEM studies. The Epoxy–Cu microcomposites are casted using hand-layout technique and cured under vacuum at room temperature. The nanocomposites have been prepared by addition of 0.2, 0.4, 0.6, 0.8, and 1.0 vol% TiB2 to Epoxy–4 vol% Cu microcomposite. Ductility has increased by 3–4 times in comparison to neat epoxy, and it has increased by 2–3 times in comparison to microcomposites. The Vickers hardness of composites shows an increasing trend with increasing particulate content. XRD studies show the intensity of amorphous epoxy phase decreasing with increasing filler content. The SEM micrographs show a uniform and dispersed distribution of Cu particles in the epoxy matrix. DSC studies reveal the glass transition temperature, Tg, of the epoxy composites to be higher than the neat epoxy and a decreasing trend is observed with increasing filler content.

The TiB2-based Fe-matrix composites fabricated using elemental powders in one step process by means of SHS combined with pseudo-HIP

The TiB2–Fe cermets with the volume fraction of Fe from 5 to 37% were fabricated from elemental powder “in situ” via SHS simultaneously with pressing by using p-HIP. The relative density, average TiB2 grain size and the Vickers hardness of composites were strongly affected by the concentration of TiB2. The maximum microhardness measured for cermet with 5vol.% of Fe reached 21.9GPa, despite essential porosity. The relative density raised significantly to 95–96%, when the volume fraction of binder increased to 25%, however at the cost of deteriorated Vickers hardness. As the result, the hardness was reduced to 3.7GPa for cermets with 37vol.% of binder. Considering the relative density, microstructure and hardness Fe addition of 20–25vol.% is optimal for TiB2–Fe cermets fabricated using this method.

Effect of Milling and Calcium Phosphate on Mechanical Properties of Nanostructured TiNbMo/CPP Biocomposites

Ti-6Al-4V ELI (Extra Low Interstitial) alloy have been widely used as alternative bone due to its excellent biocompatibility, although it still has many problems such as high elastic modulus and toxic. Therefore, biomaterial with low elastic modulus and nontoxic has to be developed. In this study, the raw materials which are nontoxic elements such as Nb and Mo were mixed and milled in a mixing machine (24h) and a high energy mechanical ball milling machine (1h, 4h and 8h) respectively. Ti-Nb-Mo-CPP composites were fabricated by spark plasma sintering (SPS) at 1000°C under 70MPa using mixed and milled powders. The effects of CPP contents and milling time on biocompatibility and mechanical property have been investigated. By X-ray diffraction (XRD), chemical reaction during the sintering was occurred and revealed new phases, Ti2O, CaO, CaTiO3, and TixPy. Vickers hardness of composites increases with increase milling time and addition of CPP contents. Biocompatibility of CPP added Ti-Nb-Mo alloys were improved.

Mechanical Properties of Ti-Nb-X-CPP Biomaterial Fabricated by Spark Plasma Sintering

Ti-6Al-4V ELI (Extra Low Interstitial) alloy have been widely used as alternative bone due to its excellent biocompatibility, although it still has many problems such as high elastic modulus and toxic. Therefore, biomaterial with low elastic modulus and nontoxic has to be developed. In this study, the raw materials which are nontoxic elements such as Nb and Mo were mixed and milled in a mixing machine (24h) and a high energy mechanical ball milling machine (1h, 4h and 8h) respectively. Ti-Nb-Mo-CPP composites were fabricated by spark plasma sintering (SPS) at 1000°C under 70MPa using mixed and milled powders. The effects of CPP contents and milling time on biocompatibility and mechanical property have been investigated. By X-ray diffraction (XRD), chemical reaction during the sintering was occurred and revealed new phases, Ti2O, CaO, CaTiO3, and TixPy. Vickers hardness of composites increases with increase milling time and addition of HA contents. Biocompatibility of HA added Ti-Nb-Si alloys were improved.

Effects of light exposure time on composite resin hardness after root reinforcement using translucent fibre post

Objectives The purpose of this in vitro study was to evaluate the Vickers hardness (VHN) of a Light Core (Bisco) composite resin after root reinforcement, according to the light exposure time, region of intracanal reinforcement and lateral distance from the light-transmitting fibre post. Methods Forty-five 17-mm long roots were used. Twenty-four hours after obturation, the root canals were emptied to a depth of 12 mm and the root dentine was artificially flared to produce a 1 mm space between the fibre post and the canal walls. The roots were bulk restored with the composite resin, which was photoactivated through the post for 40 s (G1, control), 80 s (G2) or 120 s (G3). Twenty-four hours after post-cementation, the specimens were sectioned transversely into three slices at depths of 2, 6 and 10 mm, corresponding to the coronal, middle and apical regions of the reinforced root. Composite VHN was measured as the average of three indentations (100 g/15 s) in each region at lateral distances of 50, 200 and 350 μm from the cement/post-interface. Results Three-way analysis of variance ( α = 0.05) indicated that the factors time, region and distance influenced the hardness and that the interaction time × region was statistically significant ( p = 0.0193). Tukey's test showed that the mean VHN values for G1 (76.37 ± 8.58) and G2 (74.89 ± 6.28) differed significantly from that for G3 (79.55 ± 5.18). Conclusions Composite resin hardness was significantly lower in deeper regions of root reinforcement and in lateral areas distant from the post. Overall, a light exposure time of 120 s provided higher composite hardness than the shorter times (40 and 80 s).

Effect of MgF<sub>2</sub> Additive on the Mechanical Properties in Hydroxyapatite / Zirconia Composites

In this study, the effect of MgF2 additive on the mechanical properties of hydroxyapatite (HAp)/zirconia composites was investigated. As a fluoride additive, MgF2 was added to HAp/zirconia composites for the suppression of phase decomposition from HAp to tricalcium phosphate (TCP). Due to the dissolution of MgF2 at the phase decomposition temperature of HAp, the phase decomposition of non-stoichiometric HAp was suppressed. When MgF2 (5, 10 vol%) was added to HAp/zirconia composites, the decomposition of HAp was completely suppressed below 1400oC due to the ion substitution F- of for OH- in the HAp crystal structure. The flexural strength and Vickers hardness of composites was revealed more higher values compared with the MgF2-free composites.

Influence of Solidification Microstructure and Distribution of Reinforcement on Fatigue Characteristics of Notched SiC Reinforced AC4B Alloy Composites

The influences of SiC particle distribution, surface notch size and solidification microstructure of the matrix on the fatigue characteristics of SiC reinforced JIS-AC4B alloy composites were investigated. Al–6.79 mass% Si–2.93 mass% Cu–0.17 mass% Mg–0.59 mass% Fe matrix composites with relatively homogeneously dispersed 11 mm SiC particles were fabricated through a combination of pressure infiltration and a melt stirring casting method. The matrix microstructure consisted of a dendritic alpha phase and eutectic Si with a few volume fractions of Fe intermetallic compound among the dendrites. All specimens contained some gas and shrinkage porosities, and all composite specimens contained SiC particle clusters. Vickers hardness of composites clearly increases due to the dispersion of SiC particles and age hardening. The hardening ability increases with an increasing volume fraction of SiC. Rotating bending fatigue tests were carried out on notch-free and notched specimens that had peak aging. In the notch-free matrix alloy specimen, cracks generated from porosities, whereas cracks generated from the SiC particles/the matrix interfaces in the composite specimens. Thus, the fatigue strength decreased with an increase in the SiC volume fraction. In the notch-introduced matrix alloy specimen, where the stress concentration factor is high, the notch becomes the crack generation site and dominated the fatigue strength. The cracks, however, generate near SiC particles instead of the notch bottom in the composite specimen. Moreover, it was found that the fatigue limit stress is unchanged in composite specimen even when the notch is introduced, although the critical stress for crack generation declines. Microstructural observation revealed that the cracks were spread and diverted in and around the cluster of SiC particles, suggesting that crack propagation resistance was improved in the composite specimen.

Analytical correlation of hardness and scratch adhesion for hard films

An analytical expression has been derived in order to correlate the critical load of scratch adhesion L c with hardness and film thickness for thin hard films on softer substrates, based on the model proposed by Burnett, Rickerby and co-workers (B–R model) for interpretation of composite hardness measurements. The equation was used to calculate the correlation of L c with H v(sub) (substrate Vickers hardness), H v(comp) (composite Vickers hardness), and t (film thickness) for AISI 316 stainless steel, HSS M2 and WC substrates coated with TiN films of different thickness. The calculated results were compared with experimental data for TiN films produced under similar conditions by PACVD and PAPVD deposition techniques. The present analysis yields quantitative results which agree to a satisfactory degree with experimental data in all cases considered and contribute to the understanding of the physical processes which control the deformation of the film–substrate mechanical system under scratch indentation conditions.