Papers by Keyword: Two-Stage Sintering

Abstract: The effects of sintering profiles on the Zirconia Toughened Alumina (ZTA) composite containing 0 vol% Y-TZP (pure alumina) to 20 vol% Y-TZP content prepared by a sintering method known as two-stage sintering were investigated. The heating rate was set between 10°C/min to 20°C/min, T₁ set between 1400°C to 1500°C, T₂ at 1350°C and holding time was set at 12 hours. The samples’ microstructural properties and mechanical properties, including bulk density, Vickers hardness, Young’s modulus and fracture toughness, were evaluated. Based on the data obtained, the ZTA composites with 10 vol% Y-TZP sintered at a heating rate of 10°C/min and holding time of 12 hours were able to achieve mechanical properties requirements set by the industry standard. In addition, the maximum ZTA composite’s bulk density was recorded to be above 90% T.D, while the Vickers hardness of the composite was recorded to be exceeding 17 GPa. The ZTA composite also recorded maximum Young’s modulus exceeding 380 GPa and fracture toughness above 6 MPam^1/2.

Abstract: The microstructure and mechanical properties of Zirconia Toughened Alumina (ZTA) produced via two-stage sintering at various sintering temperature of T₁ and T₂ in addition to effect of various holding time were investigated. T₁ temperature was set between the range of 1400°C to 1500°C with a heating rate of 20°C/min. The samples were then sintered at T₂ ranging from 1350°C to 1400°C followed by various holding time between 2 hours to 12 hours. The sintered samples’ microstructural properties, bulk density, hardness (Vickers hardness), elastic modulus (Young’s modulus) and fracture toughness (K_1C) were then determined. Compared to standard holding time of two-stage sintering which is 12 hours, results show that ZTA produced via two-stage sintering with shorter holding time of 4 hours with T₁ set at 1500°C and T₂ of 1450°C are capable of achieving full densification. In addition, the same sample were also able to achieve hardness up to 19 GPa, Young’s modulus of 390 GPa and fracture toughness of 6.1 MPam^1/2. The improvement in mechanical properties can be mainly attributed to the absent of surface diffusion at T₂ above 1400°C and also presence of Y-TZP which contributed to lower grain growth due to the pinning effect.

Abstract: The effect of doping small amounts of Magnesium Oxide ranging between 0 to 1 vol% on Zirconia Toughened Alumina (ZTA) composites which is one of main biomaterial used for production of total hip arthroplasty were investigated. The samples were produced via conventional two-stage sintering with T₁ varies between 1450°C and 1550°C with heating rate of 20°C/min. The samples were then rapid cooled to T₂ set at 1400°C with holding time of 12 hours. The microstructural and mechanical properties of the two-stage sintered ZTA are then investigated to determine the feasibility of MgO addition. Combination of two-stage sintering at T₁ above 1500 and also small amount of MgO up to 0.5 vol% were shown to have positive effect on ZTA which exhibited improvement on its grain size, mechanical properties such as Vickers hardness, Young’s modulus and fracture toughness compared to undoped ZTA composites. The sample with 0.5 vol% MgO addition sintered at T₁ of 1500°C and T₂ 1400°C was able to achieve Vickers hardness of 19.6 GPa, Young’s modulus of 408 GPa and fracture toughness of 6.8 MPam^1/2 without significant grain growth compared to undoped ZTA composites.

Abstract: Studies of a powder used as a modifier obtained from solid-alloy waste, such as tungsten carbide (drill balls), are presented. Dispersion, particle morphology and phase analysis of the powder were studied. The powder obtained from solid-alloy waste is a phase – it is tungsten carbide WC, it consists of nanoobjects of various shapes (nanoparticles, nanoplastics) up to 100 nm in size, with a slight presence of agglomerates up to 250 nm in size. The influence of tungsten carbide nanopowder as a modifier on the mechanical properties (strength and hardness) of PK70D3 iron-based powder structural steel has been studied. For the study, two different modes of preparation of powder alloy have been used with the use of one-stage and two-stage sintering. The influence of additive nanopowder of tungsten carbide on the mechanical properties of structural alloy powder based on iron PK70D3 has been defined: strength increases by more than 23% (in single-stage sintering), by more than 28% (in double-sintering), hardness decreases by more than 6% in single-stage sintering and increases by more than 26% with two stages of sintering, compared to the initial alloy. It has been shown that samples, obtained using double sintering with a tungsten nanopowder modifier (2.5%), have higher values of strength (more than 80%) and hardness (more than 13%), compared to modified samples, obtained by single-stage sintering technology. Thus, the modification of a 2.5 % nanoprobe of tungsten carbide, a widely used structural powder alloy based on iron PC70D3 allows for a significant change in mechanical properties. The use of powder alloys in double sintering technology provides the material hardness and the strength increase.

Abstract: It is estimated that 130 million people will suffer from osteoarthritis by 2050 which require patient to undergo a surgical procedure known as total hip replacement which has lifespan of 20 years and failure rates of ~1%. This research would highlight the effects of doping Niobium Oxide (Nb₂O₅) between 0 vol % to 0.8 vol % into Zirconia-Toughened Alumina (ZTA) composites which is the main biomaterials used to manufacture total hip arthroplasty. The samples were sintered using two-stage sintering (TSS) between 1400°C and 1550°C for first-stage sintering temperature at heating rate of 20°C/min. At second stage, the samples were sintered at 1350°C and hold for 12 hours. It was found that TSS combined with addition of Nb₂O₅ as dopants were beneficial in producing fine-grained ZTA composites with improved mechanical properties compared to undoped ZTA composites produced via TSS. Compared to undoped ZTA composites, samples doped with Nb₂O₅ and sintered at T₁ ≥1400°C were fully densed (>98%), achieved Vickers hardness more than 20 GPa and Young’s modulus higher than 410 GPa and at the same time fracture toughness of more than 8 MPam^1/2. Based on the findings, production of ZTA composites with enhanced mechanical properties with longer lifespan is possible which is beneficial in ensuring the well-being of osteoarthritis patients.

Abstract: By 2050, 130 million people are estimated to suffer from osteoarthritis worldwide which would require patients to undergo total hip replacement procedure which have a lifespan of 20 years and failure rates of ~1%. In this research, Zirconia Toughened Alumina (ZTA) which is the main biomaterial used for total hip arthroplasty were doped with varying vol % of Tantalum Oxide (Ta₂O₅) from 0 to 0.4 vol % were produced through conventional two-stage sintering with first stage sintering temperature, ranging between 1400°C and 1550°C, heated at 20°C/min, followed by second stage sintering temperature of 1350°C and hold for 12 hours. The efficacy of two-stage sintering on the microstructure and mechanical properties of the sintered samples were then evaluated. Addition of Ta₂O₅ combined with two-stage sintering were able to produce ZTA composites with enhanced grain size and mechanical properties compared to undoped ZTA composites. The samples with 0.3 vol% Ta₂O₅ content and above sintered at T₁ ≥1450°C achieved density > 99% T.D., Vickers hardness > 19 GPa, Young’s modulus > 400 GPa and fracture toughness > 6 MPam^1/2 when compared to undoped ZTA composites. This would enable production of ZTA with improved mechanical properties and lifespan ensuring the well-being of people suffering from osteoarthritis.

Abstract: The retention of nanometric microstructures is a challenge in any presureless sintering process. Grain size influences mechanical properties and grain coarsening retards densification upon sintering, thus resulting in the poor overall product properties. Hence, it is important to select, among others a suitable sintering regime which promotes densification and retards microstructure coarsening. In this work, Y-TZP ceramic bodies were fabricated under four different sintering regimes to investigate the governance of conventional Single-Stage Sintering (SSS) with 1 min and 2 h dwell time, and comparing their performance with bodies produced by Two-Stage Sintering (TSS). It was revealed that TSS sintered samples, yielded better properties than the SSS samples sintered at 1400°C with a dwell time of 2 hours. In the hydrothermal ageing test, TSS samples did not undergo the low-temperature degradation via the martensitic phase transformation of tetragonal to monoclinic symmetry. Nevertheless, it was found by XRD analysis that Y-TZP ceramics sintered by the SSS method using a short dwell time of 1 minute was effective in maintaining the tetragonal phase stability after 50 hours of exposure in superheated steam conditions.