title: The Effect of Powder Characteristics and Processing Conditions on the Microstructure and Mechanical Properties of Titanium Alloys Made by Powder Forging

authors: Jia, Mingtu

subjects: Titanium

abstract: Powder compact forging was used to produce Ti and Ti-6Al-4V rocker arms using pre-alloyed and blended elemental powders. Green powder compacts with high relative density were manufactured by warm compaction. Due to the characteristics of raw powders, interlocking and cold welding are the main mechanisms for HDH powder compaction, while warm welding is the main mechanism for GA powder compaction. During induction heating of the powder compact, it was found that necks formed extensively in as-sintered HDH Ti powder compact, leading to an average elongation to fracture of 7.5%, whereas necks did not form so extensively in as-sintered HDH Ti-6Al-4V and GA Ti-6Al-4V powder compacts, which make them brittle due to their low relative density.

As a rapid consolidation process, the densification rate was enhanced by powder compact forging due to pore collapsing caused by material flow driven by a large amount of localized plastic deformation. The degree of powder consolidation of powder compact forging using HDH Ti, HDH and GA Ti-6Al-4V powders were studied by characterising their porosity distributions, microstructure, mechanical properties and fracture behaviour. Due to the positive effect of shear deformation on the powder consolidation of powder compact forging, the powder compact in the centre of forged parts were consolidated completely with full density and had better mechanical properties than those from ingot metallurgy.

The effects of heat treatments on microstructure and mechanical properties of as-forged HDH Ti part, HDH and GA Ti-6Al-4V parts were investigated, and the ductility of forged HDH Ti part was improved significantly by annealing treatment. Recrystallization annealing was regarded as one of the best heat treatments to achieve the high ductility of as-forged HDH and GA Ti-6Al-4V parts, which can open the applications of forged HDH Ti-6Al-4V part with high oxygen content (~0.5%). The mechanical properties of forged HDH and GA Ti-6Al-4V parts after solution and aging treatment and recrystallization annealing were much better than those from both the ones from reported pre-alloyed approaches and wrought parts, which were caused by the enhancement of powder consolidation during recrystallization process.

Blended elemental approach and mechanical alloying method were applied to produce Ti-6Al-4V rocker arm by powder compact forging at 1350 oC. The effect of holding time at forging temperature on the samples produced by forging the compact of HDH Ti/Al-V master alloy powder mixture was studied, and it was found that a holding time of 5-10 minutes at forging temperature is required to get the as-forged part with good mechanical properties and homogeneous microstructure of free undissolved master alloy powders. Also, in order to reduce the holding time for achieving composition homogeneity, the powder mixture of Ti and Al-V master alloy powders was milled to produce Ti/Al-40wt%V composite powder. With such composite powder, the master alloy layers/particles were dissolved rapidly into Ti matrix, but the oxygen pick up during milling and powder passivation make the mechanical properties of the forged samples inferior to those of the parts made by powder compact forging of the powder mixture or pre-alloyed powder.

text: The Effect of Powder Characteristics and Processing Conditions on the Microstructure and Mechanical Properties of Titanium Alloys Made by Powder Forging Powder compact forging was used to produce Ti and Ti-6Al-4V rocker arms using pre-alloyed and blended elemental powders. Green powder compacts with high relative density were manufactured by warm compaction. Due to the characteristics of raw powders, interlocking and cold welding are the main mechanisms for HDH powder compaction, while warm welding is the main mechanism for GA powder compaction. During induction heating of the powder compact, it was found that necks formed extensively in as-sintered HDH Ti powder compact, leading to an average elongation to fracture of 7.5%, whereas necks did not form so extensively in as-sintered HDH Ti-6Al-4V and GA Ti-6Al-4V powder compacts, which make them brittle due to their low relative density.

As a rapid consolidation process, the densification rate was enhanced by powder compact forging due to pore collapsing caused by material flow driven by a large amount of localized plastic deformation. The degree of powder consolidation of powder compact forging using HDH Ti, HDH and GA Ti-6Al-4V powders were studied by characterising their porosity distributions, microstructure, mechanical properties and fracture behaviour. Due to the positive effect of shear deformation on the powder consolidation of powder compact forging, the powder compact in the centre of forged parts were consolidated completely with full density and had better mechanical properties than those from ingot metallurgy.

The effects of heat treatments on microstructure and mechanical properties of as-forged HDH Ti part, HDH and GA Ti-6Al-4V parts were investigated, and the ductility of forged HDH Ti part was improved significantly by annealing treatment. Recrystallization annealing was regarded as one of the best heat treatments to achieve the high ductility of as-forged HDH and GA Ti-6Al-4V parts, which can open the applications of forged HDH Ti-6Al-4V part with high oxygen content (~0.5%). The mechanical properties of forged HDH and GA Ti-6Al-4V parts after solution and aging treatment and recrystallization annealing were much better than those from both the ones from reported pre-alloyed approaches and wrought parts, which were caused by the enhancement of powder consolidation during recrystallization process.

Blended elemental approach and mechanical alloying method were applied to produce Ti-6Al-4V rocker arm by powder compact forging at 1350 oC. The effect of holding time at forging temperature on the samples produced by forging the compact of HDH Ti/Al-V master alloy powder mixture was studied, and it was found that a holding time of 5-10 minutes at forging temperature is required to get the as-forged part with good mechanical properties and homogeneous microstructure of free undissolved master alloy powders. Also, in order to reduce the holding time for achieving composition homogeneity, the powder mixture of Ti and Al-V master alloy powders was milled to produce Ti/Al-40wt%V composite powder. With such composite powder, the master alloy layers/particles were dissolved rapidly into Ti matrix, but the oxygen pick up during milling and powder passivation make the mechanical properties of the forged samples inferior to those of the parts made by powder compact forging of the powder mixture or pre-alloyed powder.

year: 2013

title: The effectiveness of an acceptance and commitment therapy self-help intervention for chronic pain

authors: Johnston, Marnie Ruth

subjects: chronic pain

abstract: Objective: To evaluate the effectiveness of an Acceptance Commitment Therapy based self-help book for people with chronic pain.
Method: This was a randomized 2 group study design. Over a 6-week period, 6 participants read the self-help book and completed exercises from it with weekly telephone support whereas 8 others formed a wait-list control group. Subsequently, 5 of the wait-list participants completed the intervention. Participants completed preintervention and postintervention questionnaires for acceptance, values illness, quality of life, satisfaction with life, depression, anxiety, and pain. Initial outcome data were collected for 8 control participants and 6 intervention participants. Including the wait-list controls, a total of 11 participants completed preintervention and postintervention measures. Whilst completing the self-help intervention, each week participants' rated the content of the book according to reading level and usefulness, and their comprehension of the content was also assessed.
Results: Compared with controls, participants who completed the book showed improved quality of life and decreased anxiety. When data from all the treatment participants were pooled, those who completed the intervention showed statistically significant improvements (with large effect sizes) for acceptance, quality of life, satisfaction with life, and values illness. Medium effect sizes were found for improvements in pain ratings.
Conclusions: These findings support the hypothesis that using the self-help book, with minimal therapist contact adds value to the lives of people who experience chronic pain.

text: The effectiveness of an acceptance and commitment therapy self-help intervention for chronic pain Objective: To evaluate the effectiveness of an Acceptance Commitment Therapy based self-help book for people with chronic pain.
Method: This was a randomized 2 group study design. Over a 6-week period, 6 participants read the self-help book and completed exercises from it with weekly telephone support whereas 8 others formed a wait-list control group. Subsequently, 5 of the wait-list participants completed the intervention. Participants completed preintervention and postintervention questionnaires for acceptance, values illness, quality of life, satisfaction with life, depression, anxiety, and pain. Initial outcome data were collected for 8 control participants and 6 intervention participants. Including the wait-list controls, a total of 11 participants completed preintervention and postintervention measures. Whilst completing the self-help intervention, each week participants' rated the content of the book according to reading level and usefulness, and their comprehension of the content was also assessed.
Results: Compared with controls, participants who completed the book showed improved quality of life and decreased anxiety. When data from all the treatment participants were pooled, those who completed the intervention showed statistically significant improvements (with large effect sizes) for acceptance, quality of life, satisfaction with life, and values illness. Medium effect sizes were found for improvements in pain ratings.
Conclusions: These findings support the hypothesis that using the self-help book, with minimal therapist contact adds value to the lives of people who experience chronic pain.

year: 2010

title: Tangi and State Funeral: Te Arikinui Dame Te Atairangikaahu and Prime Minister Norman Kirk

authors: McRae, Karyn Okeroa

subjects: Tangi

abstract: The tangi of Te Arikinui Dame Te Atairangikaahu (Te Arikinui) in 2006 paralleled the State funerals for New Zealand Prime Ministers like Norman Kirk who died in 1974. State funerals require the huge mobilization of people and resources and always attract the attention of the national and international media. The death of a Prime Minister is news worthy, but what of a minority indigenous fourth world leader like Te Arikinui? Why did her passing attract so much media attention? In this study I argue that media representation of the tangi of Te Arikinui was largely about social, cultural and symbolic capital. In media saturated societies such as Aotearoa/New Zealand, through mainstream media outlets like TV One News and the Waikato Times, Te Arikinui’s tangi event claimed a dominant space in the lives of Maori and non Maori alike. The data source includes print news media coverage of the tangi of Te Arikinui and the State funeral of Norman Kirk. Descriptive narrative and abductive analysis inform the methodology used in this study. As expected, print media reporting of both events progressed through the three stages identified by Durkheim, those of, separation, liminality and reincorporation. The ownership of death, the deceased and the continued possession of their mortal remains, itself a cultural object with symbolic and cultural capital, reflected the actual power and control of the possessor. State funerals and tangi are about the ritualized performance of grief and mourning, and require the appropriate social, cultural and symbolic capital for its enactment.

text: Tangi and State Funeral: Te Arikinui Dame Te Atairangikaahu and Prime Minister Norman Kirk The tangi of Te Arikinui Dame Te Atairangikaahu (Te Arikinui) in 2006 paralleled the State funerals for New Zealand Prime Ministers like Norman Kirk who died in 1974. State funerals require the huge mobilization of people and resources and always attract the attention of the national and international media. The death of a Prime Minister is news worthy, but what of a minority indigenous fourth world leader like Te Arikinui? Why did her passing attract so much media attention? In this study I argue that media representation of the tangi of Te Arikinui was largely about social, cultural and symbolic capital. In media saturated societies such as Aotearoa/New Zealand, through mainstream media outlets like TV One News and the Waikato Times, Te Arikinui’s tangi event claimed a dominant space in the lives of Maori and non Maori alike. The data source includes print news media coverage of the tangi of Te Arikinui and the State funeral of Norman Kirk. Descriptive narrative and abductive analysis inform the methodology used in this study. As expected, print media reporting of both events progressed through the three stages identified by Durkheim, those of, separation, liminality and reincorporation. The ownership of death, the deceased and the continued possession of their mortal remains, itself a cultural object with symbolic and cultural capital, reflected the actual power and control of the possessor. State funerals and tangi are about the ritualized performance of grief and mourning, and require the appropriate social, cultural and symbolic capital for its enactment.

year: 2010