The research involved the optimisation of various machining operations for the manufacture of automotive turbocharger impellers. Phase 1 work comprised a capability study of the Al-Si C355 impeller machining process within Doncasters Sterling. The results highlighted that both C\(_p\) and C\(_{pk}\) values were generally above the automotive industry standard of 1.66 and that current processes were capable of producing parts to specification. Benchmark testing of TiN coated WC and PCD tooling against uncoated WC was undertaken in Phase 2 experiments. While the PCD tools showed significant improvement, the TiN coated tools were inferior in terms of thrust force, torque and workpiece surface roughness when compared against the uncoated WC tools. Phase 3 research evaluated the performance of advanced diamond like carbon (DLC) coatings against WC when blind-hole drilling C355 and reaming 6082-T6 aluminium alloys. Benefits in terms of extended tool life and reduced material adhesion/BUE were observed when drilling and reaming using the commercial Graphit-iC™ coating. The performance of CVD diamond coated and PCD tools were also assessed with the latter showing lower wear rates with negligible workpiece adhesion/BUE compared to WC in both drilling and reaming experiments. The former however failed catastrophically at high cutting speeds during drilling.

No description available.

Linear friction welding (LFW) is known as an advanced technique to substitute fusion welding of joining Ni-based superalloys. However, due to the complex microstructural development caused by LFW, some unexplained issues still need to be solved, such as: influence of weld parameters (weld pressure, amplitude of oscillation, and frequency of oscillation) on the development of microstructural, microhardness, texture and residual stresses in LFWed IN718-IN713LC; impact of post-weld heat treatment (PWHT) on the microstructural and microhardness development; influence of rapid thermal cycle on the precipitate dissolution of IN718 and IN713LC; formation mechanisms of alumina inclusions (Al-oxides) on the weld interface. The present work aims to investigate these issues.

A major factor limiting the use and longevity of rare earth based magnetic materials is their susceptibility to aqueous corrosion and associated detrimental effects upon the magnetic properties of the material. This process was investigated through a combination of exposure to simulated environmental conditions and hydrogen absorption/desorption studies (HADS) in conjunction with magnetic characterisation. This study utilises NdFeB MQP-B melt-spun ribbon manufactured by Magnequench, in the form of MQI bonded magnets and also in its unbonded state as MQ powder. Specifically, it was concerned with how effective a variety of bonding media (epoxy resin,PTFE, zinc) and surface coatings (PTFE, Qsil, zinc LPPS, Dex-Cool) were at limiting the impact of aqueous corrosion in MQI bonded magnets. To characterise the effect of hydrogen absorption upon the magnetic properties of the MQP-B, hydrogen uptake was induced followed by a series of outgassing heat treatments with subsequent magnetic characterisation accompanied by HADS techniques performed after each outgas. This allowed comparisons to be made between the effects of aqueous corrosion process and hydrogen absorption upon the magnetic properties of the alloy. This study has clearly demonstrated the link between the abundance of environmental moisture and rate of Hci losses in MQI bonded magnets. In addition to this the key mechanism responsible for the degradation of magnetic properties has been identified. These losses have been attributed to the absorption of hydrogen generated by the dissociation of water in the presence of NdFeB during the aqueous corrosion process. It has been shown that the use of a bonding media that is impermeable to water can limit the effects of aqueous corrosion by limiting water access to the Magnequench particles (MQP) and also the positive effects of the use of suitable surface coatings has been shown to be effective for the same reason.

Titanium aluminide alloys are prone to extensive shrinkage porosity, particularly interdendritic layer porosity. This research aims to develop a better understanding of shrinkage porosity in Ti-46Al-8Nb alloy and how to minimize it. Practical measurements in conjunction with computer simulations were carried out in order to study the effects of cooling rate and temperature gradient on shrinkage porosity in Ti-46Al-8Nb investment castings, through investigating the influence of casting geometry, specifically mould taper on cylindrical bars, and preheating mould temperature on the macrostructure and the formation of shrinkage porosity. The interface heat-transfer coefficient of the ceramic shell/surroundings was determined using measured cooling curves obtained in 200 mbar of Argon and in vacuum. Furthermore, the alloy/mould interfacial heat transfer coefficient was estimated and was verified by comparing measured and predicted cooling curves of Ti-46Al-8Nb. The Niyama criterion function was validated to predict shrinkage-related porosity in Ti-46Al-8Nb castings, through either thermal or tilt-filling ProCastTM simulation models. Positions in a casting with Niyama values above 4 (°C. min)0.5cm-1; (3 (K. s)0.5mm-1); could be considered completely sound. The critical value of the Niyama function was 2 (°C. min)0.5cm-1; (1.5 (K. s)0.5mm-1); below which the position tested was susceptible to macroshrinkage porosity.

The response of powder of the Nickel-based superalloy CM247LC to a range of Hot Isostatic Pressing (HIPping) conditions and post-HIP heat treatments has been investigated as a preliminary step in the assessment of net shape HIPping as a possible process-route for component production. A HIPping pressure of 150MPa was used at temperatures of 1100°C, 1200°C, 1260°C and 1320°C. 1260°C as-HIPped specimens had the best tensile and HCF fatigue properties at both room temperature and 750 °C; the influence of post-HIP solution treatment conditions and of subsequent ageing on the properties of samples which had been HIPped at 1260 °C was thus investigated. A solution treatment at 1100 °C for 1h followed by forced air cooling and ageing at 870 °C for 16h resulted in the optimum tensile, high cycle fatigue at both room temperature and 750 °C. The optimized microstructure consists of a ‘necklace’ structure of coarse γ′ particles along the grain boundaries; cuboidal γ′ distributed inside grains with hyper-fine γ′ precipitated in γ channels; and fine carbides homogeneously disperse in the matrix. The properties of samples with this microstructure were comparable with those of cast, directionally solidified CM247LC. Solution treatment at 1260 °C gives better creep resistance at 760 °C/ 350MPa. It was also concluded that with gas-atomised powder, solution treatment must be carried out below the HIP temperature to minimise porosity. Analytical scanning electron microscopy showed that Hf-rich inclusions, some of which had alumina cores, initiated failure in almost all tensile samples and in all fatigue samples. It was shown that this type of inclusion can be avoided by removal of Hf from the alloy; but the removal of Hf – which is added to the alloy to improve castings – degrade the creep properties over the temperature range of 700 °C to 950 °C and the stress range of 150 MPa to 550 MPa. Further work is required to assess the influence on the tensile and fatigue properties.

The present investigation has been focused on the design, deposition and characterisation of novel low-friction, wear-resistant multilayer nanocomposite CrAlTiCN coatings. Systematic materials characterisation and property evaluation were conducted on the as-deposited and oxidation-tested CrAlTiCN coatings, and the results are presented and discussed. It is possible to generate novel CrAlTiCN coatings with the carbon content up to 24.34 at% by closed-field unbalanced magnetron sputtering of graphite target. The microstructure of the CrAlTiCN coatings mainly depends on their carbon content. When the carbon content is low, carbon atoms are mainly dissolved in the fcc metastable phase (Cr, Al, Ti) (C, N); when the carbon content is high, the major carbon atoms will form amorphous carbon with a C-C bond state and in a sp\(^2\) dominated graphitic environment. Both the hardness and brittleness of CrAlTiCN coatings reduce with increasing the carbon content. When tested at room temperature under unidirectional sliding conditions, the friction coefficient and wear of the CrAlTiCN coatings decrease with the carbon content, and the thermal stability of CrAlTiCN coatings is similar to the CrAlTiN coating but better than graphite-like carbon coatings. The good performance of the new CrAlTiCN coatings can be attributed to the optimised design of the coating system: the Cr/Al for oxidation resistance, the amorphous C for lowfriction and the multi-layered nano-composite microstructure for high toughness.

There is an urgent desire to move from lead-based piezoelectric materials to lead-free alternatives. One of the most promising lead-free materials has been reported to be zBao.7oCao.3oTi0J-(1-z) BaZro.2oTio.soOJ (abbreviated as zBCT-(1-z)BZT) system, which has comparable piezoelectric performance to lead-based materials. However, there is a lack of systematic research to investigate the effects of fabrication on the structural and functional properties of this zBCT -(1-z)BZT system. In this work, the end member Bai-xCaxTiOJ (x=0-0.30) and BaZryTii-y03 (ji=0-0.30) systems have been investigated. The phase transition diagrams of the two systems have been successfully established by measuring temperature dependent Raman spectroscopy and functional properties. The optimized fabrication procedure for forming single phased Bao.7oCao.3oTi0J and BaZro.2oTio.soOJ ceramics by solidstate methods, has been applied as a novel way to form zBCT-(1-z)BZT (O:Sz:~:J) ceramics by sintering the pre-calcined Bao.7oCao.3oTi0J and BaZro.2oTio.soOJ powders. A new phase diagram of the zBCT-(1-z)BZT (0$z:S1) has been constructed by combing structural and functional property measurements. It indicates a vertical orthorhombic phase region separating rhombohedral and tetragonal phases below the Curie temperature. The highest piezoelectric properties have been observed for z=0.5 ceramics at room temperature, due to the increased potential polarization directions in the vicinity of the orthorhombic to tetragonal phase boundary.

No description available.

No description available.