Powder metallurgy (PM) of titanium is a potentially cost-effective alternative to conventional wrought titanium. This article examines both traditional and emerging technologies, including the production of powder, and the sintering, microstructure, and mechanical properties of PM Ti. The production methods of powder are classified into two categories: (1) powder that is produced as the product of extractive metallurgy processes, and (2) powder that is made from Ti sponge, ingot, mill products, or scrap. A new hydrogen-assisted magnesium reduction (HAMR) process is also discussed. The mechanical properties of Ti-6Al-4V produced using various PM processes are analyzed based on their dependence on unique microstructural features, oxygen content, porosity, and grain size. In particular, the fatigue properties of PM Ti-6Al-4V are examined as functions of microstructure. A hydrogen-enabled approach for microstructural engineering that can be used to produce PM Ti with wroughtlike microstructure and properties is also presented.

Purpose: The diversity of biological functions makes p21Cip1/WAF1 (p21) a controversial marker in predicting the prognosis of breast cancer patients. Recent laboratory studies revealed that the regulation of p21 function could be related to different subcellular localizations of p21 by Aktinduced phosphorylation at threonine 145 in HER2/neuoverexpressing breast cancer cells. The purpose of this study was to verify these findings in clinical settings.Experimental Design: The expression status of the key biological markers in the HER2/neu-Akt-p21 pathway in 130 breast cancer specimens was evaluated by immunohistochemical staining and correlated with patients' clinical parameters and survival. In addition, an antibody against phospho-p21 at threonine 145 [phospho-p21 (T145)] was also used for better validation of these findings.Results: Cytoplasmic localization of p21 is highly correlated with overexpression of phospho-p21 (T145). Both cytoplasmic p21 and overexpression of phospho-p21 (T145) are associated with high expression of HER2/neu and phospho-Akt. Cytoplasmic localization of p21 and overexpression of phospho-p21 (T145), HER2/neu, and phospho-Akt are all associated with worse overall survival. Multivariate analysis of the Cox proportional hazard regression model revealed that cytoplasmic p21 and overexpression of HER2/ neu are independently associated with increased risk of death. Combining these two factors stratified patients' survival into four distinct groups, with a 5-year survival rate of 79% in low HER2/neu and negative/nuclear p21 patients, 60% in high HER2/neu and negative/nuclear p21 patients, 29% in low HER2/neu and cytoplasmic p21 patients, and 16% in high HER2/neu and cytoplasmic p21 patients.Conclusions: The present study, in addition to supporting the mechanisms of p21 regulation derived from laboratory investigation, demonstrates the prognostic importance of phospho-p21 (T145) for the first time and also provides a novel combination of p21 and HER2/neu for better stratification of patients' survival than any single clinicopathological or biological marker that may play important diagnostic and therapeutic roles for breast cancer patients.

Spherical titanium alloy powder is an important raw material for near-netshape fabrication via a powder metallurgy (PM) manufacturing route, as well as feedstock for powder injection molding, and additive manufacturing (AM). Nevertheless, the cost of Ti powder including spherical Ti alloy has been a major hurdle that prevented PM Ti from being adopted for a wide range of applications. Especially with the increasing importance of powder-bed based AM technologies, the demand for spherical Ti powder has brought renewed attention on properties and cost, as well as on powder-producing processes. The performance of Ti components manufactured from powder has a strong dependence on the quality of powder, and it is therefore crucial to understand the properties and production methods of powder. This article aims to provide a cursory review of the basic techniques of commercial and emerging methods for making spherical Ti powder. The advantages as well as limitations of different methods are discussed.

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Hydrogen has been investigated for decades as a temporary alloying element to refine the microstructure of Ti-6Al-4V, and is now being used in a novel powder metallurgy method known as "hydrogen sintering and phase transformation". Pseudo-binary phase diagrams of (Ti-6Al-4V)-xH have been studied and developed, but are not well established due to methodological limitations. In this paper, in situ studies of phase transformations during hydrogenation and dehydrogenation of (Ti-6Al-4V)-xH alloys were conducted using high-energy synchrotron X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The eutectoid phase transformation of b M a + d was observed in the (Ti-6Al-4V)-xH alloy via in situ synchrotron XRD at 211°C with a hydrogen concentration of 37.5 at.% (measured using TGA-DSC). The relationships of hydrogen composition to partial pressure and temperature were investigated in the temperature range 450-900°C. Based on these results, a partial pseudo-binary phase diagram of (Ti-6Al-4V)-xH is proposed for hydrogen compositions up to 60 at.% in the temperature range 100-900°C. Using the data collected in real time under controlled parameters of temperature, composition and hydrogen partial pressure, this work characterizes relevant phase transformations and microstructural evolution for practical titanium-hydrogen technologies of Ti-6Al-4V.

The development of low cost titanium metal production processes has challenged the Ti research and industrial communities around the world for decades. The strong affinity of titanium to oxygen dictates that it is very difficult to produce low-oxygen Ti metal from TiO 2 directly. In this paper, a hydrogen assisted magnesiothermic reduction (HAMR) process for producing Ti metal powder from TiO 2 powder at relatively low temperatures (750°C) is established. The overall approach is based on the thermodynamic tuning of the relative stability of MgO versus that of Ti-O solid solutions by temporarily alloying the system with hydrogen. It is shown that Ti-H-O solid solutions are less stable than their corresponding Ti-O solid solutions, which changes the reaction of Mg with Ti-O from being thermodynamically unfavorable to being favorable. The key steps for producing pure Ti metal powder from TiO 2 involve Mg reduction of TiO 2 in a hydrogen atmosphere which produces porous TiH 2 , a heat treatment procedure to consolidate the powder and reduce specific surface area of the powder, and the final step to deoxygenate the powder using Mg in a hydrogen atmosphere to further reduce the oxygen content. This paper systematically examines the changes of oxygen content, phase transformations, and the evolution of the

Powder metallurgy (PM) has been regarded as a viable and promising approach for reducing the cost of Ti fabrication because of the near-net-shape capability of PM processes. There are generally two kinds of PM approaches for making PM titanium products: blended elemental (BE) method and pre-alloyed (PA) method. [1,2] The BE method in general refers to press and sintering of BE powders. Sintering is usually carried out in high vacuum. The PA method refers to sintering PA powders, which are typically made using gas atomization or plasma rotating electrode techniques. Since PA powders have high hardness, therefore, poor press-ability if compacted using conventional uni-axial cold pressing methods, PA powders are usually consolidated using pressure assisted consolidation techniques such as hot isostatic pressing (HIP). Although, PA products in general have better mechanical properties than BE products, the costs of PA products are significantly higher: both the process for making PA powders and the processes of hot consolidation (e.g., HIP) are very expensive. Therefore, BE is still the preferred cost-effective method.However, the potential issues related to the microstructure of BE Ti such as residual porosities, oxygen contamination, and relatively coarse microstructures after sintering, limit their static and especially fatigue properties. [3] In order to eliminate porosities, reduce grain sizes and improve mechanical properties, post-sintering thermal or cold working processes are needed. Another option for removing residual porosities is to use post-sintering high pressure processes, such as HIPing, which can increase the density to greater than 99.8%. [2] Both the post-sintering thermal mechanical working and HIPing, however, add extra cost to the BE parts, reducing the cost advantages of the BE method.In recent years, an alternative BE PM Ti technique emerged which is able to produce near pore-free BE parts directly. This technique employs vacuum sintering of titanium hydride (TiH 2 ) powders instead of Ti metal powder. [4][5][6][7][8] During sintering, TiH 2 will dehydrogenate at moderate temperatures prior to being sintered at high temperatures in vacuum. Ivasishin et al. [5] showed that a blend of TiH 2 with a 10 wt% 60Al-40V master alloy powder can be sintered to 98.5-99.5% of the theoretical density in as-sintered state, in contrast to 90-95% of the theoretical density when titanium powder was used.Common to all sintered PM Ti-6Al-4V materials, the grain size of as-sintered materials are usually large consisting of coarse Widmanstätten lamellar alpha plate colony structures, [1,2,5] and the coarse microstructure is detriment to tensile ductility and fatigue mechanical properties. The as-sintered coarse microstructures can be refined only by post-sintering thermal mechanical working and heat treatments, which, once again, would increase the cost of PM Ti parts, reducing the economic benefits of PM Ti.In order to overcome the trade-off between performance and cost, an ''ideal'' PM Ti process must be able to...

Reactive metals including Ti, Zr, Hf, and V, among others, have a strong chemical affinity to oxygen, which makes them difficult to produce and costly to use. It is especially challenging to produce pure or metal alloy powders of these elements when extremely low oxygen content is required, because they have high solubility for oxygen, and the solid solution of these metals with oxygen is often more stable thermodynamically than their oxides. We report a novel thermochemical approach to destabilize Ti(O) solid solutions using hydrogen, thus enabling deoxygenation of Ti powder using Mg, which has not been possible before because of the thermodynamic stability of Ti(O) solid solutions relative to MgO. The work on Ti serves as an example for other reactive metals. Both analytical modeling and experimental results show that hydrogen can indeed increase the oxygen potential of Ti-O solid solution alloys; in other words, the stability of Ti-O solid solutions is effectively decreased, thus increasing the thermodynamic driving force for Mg to react with oxygen in Ti. Because hydrogen can be easily removed from Ti by a simple heat treatment, it is used only as a temporary alloying element to destabilize the Ti-O systems. The thermodynamic approach described here is a breakthrough and is applicable to a range of different materials. This work is expected to provide an enabling solution to overcome one of the key scientific and technological hurdles to the additive manufacturing of metals, which is emerging rapidly as the future of the manufacturing industry.