Materials Science Forum Vols. 618-619

Abstract: Abstract The effects of hydrogen on the hydrogen embrittlement of Ti-2Al-2.5Zr alloy was investigated by tensile test, slow strain rate test (SSRT), and the amount of absorbed hydrogen of Ti-2Al-2.5Zr alloy was studied by immersion test in alkaline steam water at a pressure of 8.5MPa. The results indicated that the hydrides(TiH2) in Ti-2Al-2.5Zr alloy formed as platelets and were identified as face-centered cubic δ-hydride. At room temperature, hydrogen and formed hydrides induced increase of the intensity and caused loss in the ductility. In alkaline steam water at a pressure of 8.5MPa, the hydrogen embrittlement susceptibility index (IHE) of Ti-2Al-2.5Zr alloy increased with increasing hydrogen content, and the IHE value of the alloy with 350ppm H was less than 0.1. Moreover the amount of absorbed hydrogen of Ti-2Al-2.5Zr alloy increased with increasing of immersion time, and absorbed hydrogen was still less than 50ppmH even when immersion time reached 13000h.

Abstract: A Ti-10wt.%Mg powder alloy has been produced by mechanical alloying. Elemental powders of Ti and Mg were ball milled in a Zoz-Simoloyer CM01 for 16 and 20 hours under argon. Mechanical alloying was followed by XRD, SEM and particle size analysis. Test specimens of the milled powders were produced by cold compaction and sintering (under argon). The milling resulted into a fcc TiMg solid solution for both milling durations. Sintering leads to a partial decomposition of the fcc TiMg to hcp TiMg and Ti.

Abstract: Porous metal fiber media have traits of metal materials and functional materials. Porous metal fiber media are gaining popularity in engineering applications due to their special properties, such as lower density, larger specific surface area, higher mechanical strength and excellent permeability. In this paper, the recent development of fabrication methods and the various properties of porous metal fiber media were reviewed. Porous metal fiber media are divided into structural and functional applications. The mechanical and physical properties of porous metal fiber media, including tensile property and compressive property were analyzed. Porosity and the sintering process play an important role in the mechanical properties of porous metal fiber media.

Abstract: The microstructural changes of alpha morphology in Ti-17 alloy with an initial lamellar microstructure were examined quantitatively using image analysis software. The alpha morphology changes at different locations (center, edge, 0.5R) of the cakes deformed to different strain level were measured by Feret ratio and related to the imposed strain estimated using finite element analysis. It was found that the modification of alpha morphology depended strongly on the forging strains and the locations in the cakes. The distribution curve of Feret ratio was characterized by a single peak at Feret ratio between 1.5-2.5. These peak values increased with the increase in the height reductions. Increasing forging strains caused the high-Feret-ratio lamellae to decrease but low-Feret-ratio alpha to increase noticeably. The average strains for initiation of globalization were of the order of 0.4 and those for completion were of the order of 1.0, which was lower than conventional α+β titanium alloys.

Abstract: Advances have been made in the art of metal cutting, much to the economic benefit of industrialized nations. Not withstanding this, engineers continue to seek stronger and lighter materials. New challenges emerge as we seek to understand and control the deformation of a small volume of material in the immediate vicinity of the cutting edge. In this paper we use a metallurgical approach to explore and understand the nature of high strain deformation in light metals and its influence on the chip forming process. In particular the phenomenology of material flow around the cutting edge is discussed on the basis of previous studies of machining in the SEM. The issue of chip separation is discussed, particularly in relation to its impact on the tribology of the ship / tool / workpiece interface. The objective is to better design cutting tools and their vapour deposited coatings for improved machinability in light metals.

Abstract: The aero-engine has provided the major drive for the development of new improved titanium alloys in recent years. This paper covers these developments from the workhorse alloy Titanium 6/4 and it’s higher temperature stable mates through to the more exotic intermetallic materials and on to their reinforcement with ceramics. The use of Ti6/4 alloy is now widespread throughout the aero space industry providing a good combination of strength at moderate temperatures (~300°C) a relatively low density and a wide range of processing options ranging from castings to forgings to powder HIP and diffusion bonding. Alloy development for the aero-engine essentially concentrated on either increasing the temperature capability and creep resistance or increasing the strength at intermediate temperatures. Alloys such as Ti 6242 and IMI 834 were aimed at compressor disc applications with operation up to around 600°C. Improvements resulted from compositional control and thermal processing to optimize the microstructure for creep and fatigue. High strength intermediate temperature capability (~500°C) alloys were also developed (Ti6246) where higher levels of molybdenum balance the alpha strengthening additions. The drive for lighter weight led to the development of titanium intermetallic systems. Alloys such as 45-2-2XD and Alloy 7 have been the subject of much research and manufacturing development over the last 20 years, demonstrating that they are capable of operating at temperatures well above those of conventional titanium. More recently, alloys with higher additions of Nb and Ta have shown improved mechanical properties and offer promise to extend the application of TiAl above 700°C. In parallel with intermetallic developments combining titanium alloys with the extreme high strength of ceramic fibres has proved irresistible and many ways to produce titanium composites have been developed. The majority of application development has focused on Ti6/4 alloy as the matrix although other matrix alloys have been investigated and tested in U.S. engine demonstrators. Recently a combination of Ti-22Al-26Nb disks reinforced with orthorhombic MMC ran for over 100 hours in an engine test. However, none of these niche composite systems has yet made the transition into large volume production and the fibre reinforced Ti6/4 system probably offers the greatest potential for implementation. The main barrier to the take up of both advanced intermetallics and titanium composites is the cost of raw materials and processing. The challenge still exists to produce net shape components and provide weight savings at an acceptable cost. This will be the key to future exploitation.

Abstract: Recent advances in synthesis of titanium (Ti) alloy powders by direct reduction methods (meltless Ti) have led to new opportunities to produce Ti alloys with enhanced capabilities. The meltless Ti alloy powders can be consolidated into mill products, or used to manufacture near-net shape (NNS) components. A vision is outlined for creation of a new supply chain producing meltless Ti alloy powders, leading to the production and application of innovative turbine engine components. This paper highlights the benefits of meltless Ti alloys, details current assessment of meltless Ti alloy technology, and outlines some of the challenges to fully establish the new supply chain.

Abstract: Major research and development efforts both in CSIRO and elsewhere aim to develop processes for commercial production of low cost titanium powder. These processes could reduce the current cost of titanium, but the major savings are expected to come by enabling powder metallurgical processes which transform these powders into products. Powder metallurgical (PM) processes (e.g. CIP/HIP) are well established for discrete components, but technologies for continuous production of “mill” product are immature. New processes will be needed for the economic manufacture of mill product (e.g. sheet and tube) from the large quantities of low-cost powder which will become available when the emerging powder production processes enter commercial production. The paper will present a process for the production of commercial purity (CP) sheet by direct rolling of powder. It is novel in that it avoids both the use of binders and densification via batch sintering. A roll compacted green sheet is rapidly heated under a controlled atmosphere before being consolidated to nominally 100% density by hot rolling. Following conventional batch annealing, strip samples exhibit properties approaching those of commercial wrought sheet of an equivalent grade. In order to achieve this, a number of key variables including powder chemistry, morphology and particle packing, the roll compaction and hot rolling parameters needed to be understood and closely controlled.

Abstract: The aim of this work is to develop a 3-D transient finite element model for a moving Gaussian laser heat source to predict the depth of the heat-affected zone (HAZ) and temperature distribution in a Ti6Al4V alloy workpiece. It is found that the temperature profile and depth of HAZ are strongly dependent on the parameters of the laser beam. The thermal model simulations are compared with results produced by experimental work and these show close agreement.

Abstract: Through focused investment by the CSIR, the South African Innovation Fund, the Automotive Industry Development Centre and the Department of Science and Technology over the past eight years, the national Light Metals Development Network has been established and grown into a well aligned collaborative research and development programme. The research and development focus has been primarily on aluminium and titanium technologies as applied in the automotive and aerospace industry sectors, with the latter growing in prominence over the past three years. Since 2009 the titanium-related research and development activities have been consolidated in a Titanium Centre of Competence. This paper provides an overview of the current status of the programme, the R&D focus areas, the collaborating entities and the industry involvement. It also highlights some of the significant achievements of the network and notable outputs produced. The Titanium Centre of Competence as a vehicle for strengthening industrial research and innovation capabilities in specific fields of technology is discussed and some initial experiences are shared.