Papers by Keyword: Hot Isostatic Pressing (HIP)

Abstract: The high temperature oxidation behaviors of the Ti3SiC2-SiC ceramic composites fabricated by in situ synthesis under hot isostatic pressing were studied by DSC. The results show that the growth of the oxide scales on Ti3SiC2-SiC ceramic composites obeys a parabolic law in air. The oxidation resistance at 1400°C is better than that at 1200°C for long time. The oxidation resistance of the Ti3SiC2-SiC ceramic composites is much higher than that of monolithic Ti3SiC2. The mechanism of oxidation of Ti3SiC2-SiC ceramic composites is discussed.

Abstract: AlN-SiC-TiB2 ceramics were synthesized by self-propagating high temperature synthesis (SHS) and hot isostatic pressing (HIP) methods. The powder mixtures of Al, 6H-SiC and TiB2 were shaped by isostatic cool pressing method, and then combustion reaction was carried at the pressure of 100-200 MPa N2 by an ignitor. The solid solution of AlN and 2H-SiC in AlN-SiC-TiB2 ceramics was formed. The phase composition and microstructure were investigated by XRD and SEM. The mechanical properties of composite were measured as functions of composition. The maximum value of flexural strength and fracture toughness of composites were 430 MPa and 3.9 MPa⋅m1/2 respectively.

Abstract: The fabrication of AlN-SiC-TiB2 ceramics with powder mixtures of Al, 6H-SiC and TiB2 was investigated by self-propagating high temperature synthesis (SHS) and hot isostatic pressing (HIP). The powder mixtures were shaped by isostatic cool pressing method and the combustion reaction was carried at the pressure of 100-200 MPa N2 by an ignitor. The compositions and morphologies of the combustion product were studied by XRD and SEM. The determined bending strength and the fracture toughness of the ceramics were 350 MPa and 3.5 MPa⋅m1/2 respectively.

Abstract: Microporosity in both HIPped and non-HIPped unmodified aluminum cast alloy A356-T6 was quantified metallographically in terms of its area, area percentage, length, sphericity and perimeter. In the studied materials, the secondary dendrite arm spacing (SDAS) values vary from 82μm to 96μm for both the HIPped and the non-HIPped castings. HIPping process significantly reduces porosity area fraction and pore sizes. The maximum area fraction of porosity and maximum pore area of the non-HIPped specimens are increased with increasing SDAS.

Abstract: BN-AlN-TiB2 compound conductive ceramics from powder mixtures of BN, Al, and TiB2 was fabricated by self-propagating high temperature synthesis (SHS) and hot isostatic pressing (HIP). The powder mixtures were shaped by isostatic cool pressing at 5-10MPa and the combustion reaction was carried at 100-200 MPa N2 by an ignitor. XRD experiments confirmed that the reaction was complete and only AlN, BN and TiB2 were detected. Optical microscopy as well as SEM with an electron probe microanalysis was used for microstructural analysis and revealed a relatively uniform distribution of particulates. The temperature-dependence and composition-dependence of the electrical resistivity of BN-AlN-TiB2 ceramics were studied. The results showed that the optimum composition was 5-10wt% BN, 30-55wt% Al and 60-40wt% TiB2, and the products had the density of 90% of the theoretical, resistivity of 80-1000 μ⋅cm and bending strength of 100-200 MPa.

Abstract: In this paper, transparent polycrystalline magnesium aluminate spinel was fabricated by hot pressing ultra fine high purity spinel powder using LiF as the sintering aid in vacuum, then hot isostatic pressing (HIPing) the sintered body to improve the optical properties of the sample. The transmittance and the strength of the samples before and after HIPing were measured; morphologies of the fracture surface of the samples before and after HIPing were observed. Following hot pressing, the grain size of the sample is small; the transmission values are low and may varied at different sites in the same sample. After HIPing, the strength of the sample decreased, the grain size increased obviously, and the transmittance and the uniformity of transmittance increased significantly. The panel of transparent spinel up to 200 mm in diameter and 8 mm thick was fabricated by this method; the average transmittance of the spinel is above 80% in the range between 2 μm and 5 μm .

Abstract: Total hip arthroplasty (THA) in patients with sequelae of the hip joint infection is a technically challenging procedure. In addition, the majority of such patients are less than fifty years old, so it has been reported that they have higher prevalence of complication and failure of component fixation. Alumina-on-alumina couplings are an attractive alternative and may offer a promising option for such young active patients. We analyzed 33 primary cementless alumina-onalumina THAs (PLASMACUP®SC-BiCONTACT® system incorporating BIOLOX® forte) that had been performed in patients who had sequelae of the hip joint infection. The average age of the patients was 37.8 years (range, 19-68 years) and 26 patients were younger than 50 years old. They were followed-up for more than 5 years (average, 74 months; range, 60-93 months). All hips had no recurrence of hip joint infection. The mean Harris hip score improved from 59.8 points to 93.5 points. All of the implants had radiographic evidence of a bone ingrowth and no radiological loosening was found. During the follow-up period, no cup or stem was revised and no periprosthetic osteolysis was observed. Nonunion of the osteotomized greater trochanter occurred in one hip, but no postoperative infection or ceramic failure was observed. The 5-year minimum follow-up clinical results of modern alumina-on-alumina THAs performed in patients with sequelae of the hip joint infection were encouraging with regard to osteolysis and implant stability. Our findings show that this alternative articulation offers a reliable solution for these young patients with long-standing anatomic abnormalities of the bone and soft tissues.

Abstract: Due to their better mechanical and physical properties diamond tools have largely replaced cemented carbide tools for machining of mineral materials like concrete and rocks. The decomposition tendency of diamond has to be taken into consideration during the manufacturing process as well as during their employment in machining tools. By using water cooling the diamond decomposition is reduced, but the contamination of occupied buildings by concrete/rock-watermixture and the need of water supply units on building sites are unfavourable. However, absence of water cooling lead to an increased tribological and thermal wear of conventional diamond tools. Due to the heat development the diamonds in direct contact with mineral materials as well as the diamonds in deeper layers are deteriorated. The Institute of Materials Engineering pursues a novel thermal protection shield concept, in which thermal insulating materials such as Al2O3, ZrO2 or glass in diamond impregnated composite structures act as heat shield, which protects diamonds in deeper layers against high temperature and graphitisation. Before the effectiveness of this concept could be investigated suitable composites have to be manufactured. In this paper the powder metallurgical production processes of diamondalumina- cobalt-composites with varying alumina and cobalt particle sizes, their microstructures and porosities are described. In comparison to composites with larger alumina particle sizes it could be observed that the distribution of alumina particles with particle sizes below 70 ,m in the cobalt matrix is uniform and the porosity of the composite decrease.

Abstract: We sintered α (6H)- and β(3C)-SiC powders using an Al-B-C additive. SiC powders were densified to > 98% of the theoretical density from 1950 to 2150oC with 0.67-2.7 mass % AlB2 and 2.0 mass % C. Sintering temperatures are 150-200 oC lower than the conventional. During sintering, 6H polytype in α-SiC powder was partly transformed to 4H. α-SiC powder grew moderately into plate-shaped grains. β-/SiC powder was completely transformed to 6H and subsequently 4H with large grain growth. Low-temperature sintering enabled us to use hot isostatic pressing resulting in pore-free SiC materials.