Re-examination of the effect of NbC precipitation on shape memory in Fe-Mn-Si-based alloys

Current literature pertaining to the shape memory effect in the Fe–Mn–Si-based system is critically discussed. It is argued that the
enhanced shape memory previously attributed to NbC precipitation is mainly due to the associated thermo-mechanical treatments.
It is concluded that the thermo-mechanical processing of the alloy is the dominant factor that determines the shape memory effect in
this alloy system.

Texture and mechanical anisotropy in three extruded magnesium alloys

One ZM61 alloy (6·2%Zn, 1·2%Mn) and two magnesium alloys containing nominally 3% of neodymium and yttrium respectively have been prepared in the form of hot extruded flat strips. Their textures and microstructures have been quantified and series of mechanical tests were carried out to determine plane stress yield loci in both the solution treated and aged conditions. The ZM61 alloy had a sharp texture and marked anisotropy of strength that could be rationalised in terms of deformation by basal <a> slip and {1012}<1011> twinning. This material was much weaker in compression than in tension. Precipitation hardening on aging caused a greater impedance to twinning than to slip with the result that the anisotropy was somewhat reduced. The Mg–3Nd alloy had a very weak and different texture but nevertheless demonstrated a pronounced anisotropy of strength. Aging increased the yield stress by about 80% and also inhibited twinning to some extent although the degree of anisotropy remained almost unaffected. The Mg–3Y alloy which showed a texture of intermediate strength was different in type from either of the others. Its strength behaviour was close to isotropic; in particular, no difference existed between tensile and compressive loading, and aging produced only a marginal increase in strength. Twins were relatively infrequent in the deformed Mg–3Y alloy but its mechanical behaviour could not be rationalised according to simple models.

Some issues relating to the ductility of wrought magnesium alloys

The present work is concerned with gaining a better understanding of the factors that control the ductility of wrought magnesium alloys. The ultimate aim is to develop alloys with vastly improved room temperature formability. It is shown that 3D tomography of fractured tensile specimens reveals disk shaped voids aligned more or less at 45 deg. to the tensile axis. These voids are consistent with twin induced void formation. It is also shown that the double twins that produce such voids form in contradiction to Schmid predictions. Finally, it is demonstrated that low levels of rare-earth additions leads to vastly improved texture and ductility in extrusions, as they do in rolled sheet.

The microstructure evolution and mechanical properties of cryorolled Al alloys

A solutionized Al2024 alloy was subjected to rolling at liquid nitrogen temperature (cryorolling) resulting in an ultra-fine stmcture. The material was also subjected to recovery annealing at 160°C. The ultrafine structured material demonstrated increased strength but very low ductility. The uniform elongation of the material after recovery annealing increased without any sacrifice of strength.

Australian dental policy reform and the use of dental therapists and hygienists

Oral diseases including dental caries and periodontal disease are among the most prevalent and costly diseases in Australia today. Around 5.4% of Australia’s health dollar is spent on dental services totalling around $2.6 billion, 84% of which are delivered through the private sector (AIHW 2001). The other 16% is spent providing public sector services in varied and inadequate ways. While disease rates among school children have declined significantly in the past 20 years the gains made among children are not flowing on to adult dentitions and our aging population will place increasing demands on an inadequate system into the future (AHMAC 2001). Around 50% of adults do not received regular care and this has implications for widening health inequalities as the greatest burden falls on lower income groups (AIHW DSRU 2001). The National Competition Policy agenda has initiated, Australia-wide, reviews of dental legislation applying to delivery of services by dentists, dental specialists, dental therapists and hygienists and dental technicians and prosthetists. The review of the Victorian Dentists Act 1972, was completed first in 1999, followed by the other Australian states with Queensland, the ACT and the Northern Territory still developing legislation. One of the objectives of the new Victorian Act is to ‘…promote access to dental care’. This study has grown out of the need to know more about how dental therapists and hygienists might be utilised to achieve this and the legislative frameworks that could enable such roles. This study used qualitative methods to explore dental health policy making associated with strategies that may increase access to dental care using dental therapists and hygienists. The study used a multiple case study design to critically examine the dental policy development process around the Review of the Dentists Act 1972 in Victoria; to assess legislative and regulatory dental policy reforms in other states in Australia and to conduct a comparative analysis of dental health policy as it relates to dental auxiliary practice internationally. Data collection has involved (I) semi-structured interviews with key participants and stakeholders in the policy development processes in Victoria, interstate and overseas, and (ii) analysis of documentary data sources. The study has taken a grounded theory approach whereby theoretical issues that emerged from the Victorian case study were further developed and challenged in the subsequent interstate and international case studies. A component of this study has required the development of indicators in regulatory models for dental hygienists and therapists that will increase access to dental care for the community. These indicators have been used to analyse regulation reform and the likely impacts in each setting. Despite evidence of need, evidence of the effectiveness and efficiency of dental therapists and hygienists, and the National Competition Policy agenda of increasing efficiency, the legislation reviews have mostly produces only minor changes. Results show that almost all Australian states have regulated dental therapists and hygienists in more prescriptive ways than they do dentists. The study has found that dental policy making is still dominated by the views of private practice dentists under elitist models that largely protect dentist authority, autonomy and sovereignty. The influence of dentist professional dominance has meant that governments have been reluctant to make sweeping changes. The study has demonstrated alternative models of regulation for dental therapists and hygienists, which would allow wider utilisation of their skills, more effective use of public sector funding, increased access to services and a grater focus on preventive care. In the light of theses outcomes, there is a need to continue to advocate for changes that will increase the public health focus of oral health care.

In vitro cytotoxicity of binary TI alloys for bone implants

Interest in using titanium (Ti) alloys as load-bearing implant materials has increased due to their high strength to weight ratio, lower elastic modulus, and superior biocompatibility and enhanced corrosion resistance compared to conventional metals such as stainless steel and Co-Cr alloys. In the present study, the in vitro cytotoxicity of five binary titanium alloys, Ti15Ta, Ti15Nb, Ti15Zr, Ti15Sn and Ti15Mo, was assessed using human osteosarcoma cell line, SaOS-2 cells. The Cell proliferation and viability were determined, and cell adhesion and morphology on the surfaces of the binary Ti alloys after cell culture were observed by SEM. Results indicated that the Ti binary alloys of Ti15Ta, Ti15Nb and Ti15Zr exhibited the same level of excellent biocompatibility; Ti15Sn alloy exhibited a moderate biocompatibility while Ti15Mo alloy exhibited a moderate cytotoxicity. The SaOS-2 osteoblast-like cells had flattened and spread across the surfaces of the Ti15Ta, Ti15Nb, Ti15Zr and Ti15Sn groups; however, the cell shapes on the Ti15Mo alloy was shrinking and unhealthy. These results indicated that the Mo contents should be limited to a certain level in the design and development of new Ti alloys for implant material applications.

Optimization of alloy design and hot rolling conditions for shape memory in Fe–Mn–Si-based alloys

The effect of composition and hot rolling conditions on the shape memory effect (SME) in the Fe–Mn–Si-based system has been studied to obtain improved shape memory without the need to rely on “training”. It has been found that the texture is not markedly affected by rolling conditions, and texture is therefore not a major factor in explaining variations in SME with processing conditions. Decreasing the pre-deformation temperature to below the Ms was found to have a beneficial effect on shape memory. It was found that the best SME was achieved in an alloy that had Ms just above room temperature, and had been processed by hot rolling followed by recovery annealing. Alloys of different compositions exhibited different optimum rolling temperatures for maximum shape memory performance.

Effect of second-phase particles on shape memory in Fe-Mn-Si-based alloys

The shape memory behaviour of two Fe–Mn–Si-based alloys has been investigated. One alloy was a reference alloy, and the other alloy was
similar in composition except that it contained 0.55 wt% Ti. Following solution treatment and quenching, strip samples were subjected to three types
of treatments; isothermal holding, cold rolling followed by isothermal holding, and hot rolling followed by isothermal holding. These treatments
resulted in the formation of intermetallic precipitates in the Ti-containing alloy, while the reference alloy remained precipitate-free. In comparing
the shape memory of the reference and the particle-containing alloy after identical heat treatments, it was found that the formation of precipitates
had a beneficial effect on the shape memory in all cases. In general, the larger precipitates caused a larger increase in the shape memory. The effect
of particle size on shape memory has been analysed using the current data and published results for a range of precipitate types.

Austenite stability in Fe-Mn-Si-based shape memory alloys

The stability of austenite in a number of Fe–Mn–Si-based shape memory alloys has been investigated. It was found that a grain boundary precipitate of BCC structure is formed over a wide range of alloy compositions and heat treatment temperatures. This grain boundary phase has been identified as the chi (χ) phase. Although up to 3 vol.% of the grain boundary precipitate was generated by isothermal aging in the range 500–800 °C, it was found not to markedly affect the mechanical properties or the shape memory effect. Nano-indentation indicated that the hardness and strength of the parent and precipitate phase are very similar, as are their compositions.

Processing and mechanical properties of open-cell Mg alloys

Mechanical properties of open-cellular magnesium alloys with three types of
geometric cell-structures, that is, a random round cell-structure (type A). a controlled diamond cell-structure for which the angle between the struts and the load direction is 45 degree (type B) and a controlled square cell-structure for which the angle between the struts and the loading direction is 0 degree (90 degree) (type C), are investigated by compressive tests. Results indicate that type C showed a higher collapse stress than the other two types. The collapse mechanism and the effects of the loading direction on collapse stress for the three types of magnesium alloys arc discussed from the viewpoint of bending, buckling and yielding of the struts. It is suggested that collapse for the open-cellular magnesium aHoys is associated with yielding of struts

Theory of planned behaviour and implementation intentions in dental attendance

The thesis used a model of health behaviour to examine the predictors of dental attendance. Older respondents who had strong intentions, low perceived vulnerability, stable plans to attend, and were influenced by significant others were more likely to have attended the dentist for preventive care in the last 12 months. The portfolio concludes that attachment theory is a useful conceptual framework for enhancing our understanding of the antecedents and consequences of childhood sexual abuse.

Atom probe tomography of solute distributions in mg-based alloys

Atom probe tomography (APT) has been carried out on three magnesium-based alloys: M1 (Mg-1 wt pct Mn), AZ31(Mg-3 pct Al-1 pct Zn), and ME10 (Mg-1 pct Mn- 0.4 pct misch metal). The aims of this experiment were to measure the composition of the matrix and to investigate solute clustering in the matrix of the three different alloys. For AZ31, the matrix composition was variable but close to the bulk composition. For ME10 and M1, the matrix was depleted in alloying additions, with the remainder residing in precipitates. Most alloying additions were found to exhibit clustering to some extent, with misch metal having the strongest partitioning behavior to clusters. Solute clusters did not appear to affect mechanical twinning. It has been proposed that the clustering behavior of misch metal contributes to its ability to modify the recrystallization texture.

Role of grain boundary sliding in the anisotropy of magnesium alloys

The plastic anisotropy of magnesium alloy sheet drops rapidly with test temperature. It has previously been suggested that this may be due to an increase in the activity of (c+a) dislocations. The present note points out that the phenomenon may result, instead, from the action of grain boundary sliding. This can explain the strong effect of grain size on anisotropy. Furthermore, it points to a new avenue for alloy development.