Effect of Carbon Reduction on the Toughness of 9CrWVTaN Steels

Nitride-strengthened, reduced activation, martensitic steel is anticipated to have higher creep strength because of the remarkable thermal stability of nitrides. Two nitride-strengthened, reduced activation martensitic steels with different carbon contents were prepared to investigate the microstructure and mechanical property changes with decreasing carbon content. It has been found that both steels had the microstructure of full martensite with fine nitrides dispersed homogeneously in the matrix and displayed extremely high strength but poor toughness. Compared with the steel with low carbon content (0.005 pct in wt pct), the steel with high carbon content (0.012 pct in wt pct) had not only the higher strength but also the higher impact toughness and grain coarsening temperature, which was related to the carbon content. On the one hand, carbon reduction led to Ta-rich inclusions; on the other hand, the grain grew larger when normalized at high temperature because of the absence of Ta carbonitrides, which would decrease impact toughness. The complicated Al2O3 inclusions in the two steels have been revealed to be responsible for the initiated cleavage fracture by acting as the critical cracks.

Cast Offs (Touchstones in Practice)

The working process of an architect is not often shown publicly, as the finished buildings, more particularly images and publications on them tend to dominate how architecture is communicated. In this there is something lost. The experience of the building, which is its most valuable aspect, is only possible by being there physically. Photography and other means of representation of architecture can tend to an overly perfected and artificial read of both the building and how the design was produced. In truth the design process for a building is a complex one, full of chance discoveries, multiple abandoned ideas, and refinement which is lateral as well as rational.

When we were asked to exhibit it struck us that we should address this deficit in some small way. These are models made as part of the design process for four projects (an arts centre, a womens refuge, a villa and four artists studios). An important part of our work method is to try to explore the material qualities of the buildings we are working on. To advance this we commonly make models to allow us to make discoveries and to advance the project so that the finished building is imbued with material and spatial character. These models are not made to show the final design of the building but to highlight an aspect that we are interested in exploring, in some cases this is about a space, in others about texture and its relationship to form. We chose these four models as all in some way allowed us to make discoveries about the project being explored. This discovery, once made, is what we value. The model itself serves only to produce this, and once made we can cast off the model and move on. We show them, not as architecture, but as touchstones for ideas out of which architecture may come.

Microabrasion-corrosion of cast CoCrMo alloy in simulated body fluids

Wear and corrosion of metal-on-metal hip replacements results in wear debris and metal-ion release in vivo, which may subsequently cause pain and hypersensitivity for patients. Retrieved metal-on-metal hip replacements have revealed that two-body sliding wear and three-body abrasive wear are the predominant wear mechanisms. However, there is a lack of understanding of the combined effects of wear/corrosion, especially the effect of abrasion-corrosion.

This study investigates the sliding-corrosion and abrasion-corrosion performance of a cast CoCrMo alloy in simulated hip joint environments using a microabrasion rig integrated with an electrochemical cell. Tests have been conducted in 0.9% NaCl, phosphate buffered saline solution, 25% and 50% bovine serum solutions with 0 or 1 g cm(-3) SiC at 37 degrees C. Experimental results reveal that under abrasion-corrosion test conditions, the presence of proteins increased the total specific wear rate. Conversely, electrochemical noise measurements indicated that the average anodic current levels were appreciably lower for the proteinaceous solutions when compared with the inorganic solutions. A severely deformed nanocrystalline layer was identified immediately below the worn surface for both proteinaceous and inorganic solutions. The layer is formed by a recrystallisation process and/or a strain-induced phase transformation that occurs during microabrasion-corrosion. (C) 2008 Elsevier Ltd. All rights reserved.