The effects of increasing the nickel content from 3 to 7 or 9 wt-% were investigated in high strength steel weld metals with 2 wt-% manganese. Nickel additions were beneficial to strength but detrimental to impact toughness. Significant segregation of nickel and manganese to interdendritic regions was observed at the two higher nickel contents. In these weld metals a mainly martensitic microstructure developed at interdendritic regions, whereas bainite was found at dendrite core regions. The microstructural inhomogeneity was due to segregation and the accompanying stabilisation of austenite in solute enriched regions to lower transformation temperatures. With 3 wt-% nickel the microstructure was found to be more homogeneous, with mainly bainite forming. The decrease in impact toughness with increasing nickel content was mainly attributed to the formation of coarse grained coalesced bainite.

Nanoparticles (NPs) comprised of nanoengineered complexes are providing new opportunities for enabling targeted delivery of a range of therapeutics and combinations. A range of functionalities can be included within a nanoparticle complex, including surface chemistry that allows attachment of cell-specific ligands for targeted delivery, surface coatings to increase circulation times for enhanced bioavailability, specific materials on the surface or in the nanoparticle core that enable storage of a therapeutic cargo until the target site is reached, and materials sensitive to local or remote actuation cues that allow controlled delivery of therapeutics to the target cells. However, despite the potential benefits of NPs as smart drug delivery and diagnostic systems, much research is still required to evaluate potential toxicity issues related to the chemical properties of NP materials, as well as their size and shape. The need to validate each NP for safety and efficacy with each therapeutic compound or combination of therapeutics is an enormous challenge, which forces industry to focus mainly on those nanoparticle materials where data on safety and efficacy already exists, i.e., predominantly polymer NPs. However, the enhanced functionality affordable by inclusion of metallic materials as part of nanoengineered particles provides a wealth of new opportunity for innovation and new, more effective, and safer therapeutics for applications such as cancer and cardiovascular diseases, which require selective targeting of the therapeutic to maximize effectiveness while avoiding adverse effects on non-target tissues.

Microstructures, and hence mechanical properties, of high strength steel weld metals are affected by cooling rate. Weld metal microstructures for a nominal composition of Fe-0?05C-0?3Si-2Mn-3Ni-0?5Cr-0?6Mo (wt-%) were therefore characterised for a range of cooling rates using high resolution scanning electron microscopy, and transformation behaviour, assessed from cooling curves, is presented as a continuous cooling transformation diagram. As deposited last bead microstructure changes gradually from lower bainite and martensite interspersed with coalesced bainite, via a mixture of relatively fine upper and lower bainite, to coarse upper bainite as cooling rate decreases. The microstructure of reheated beads follows the as deposited structure closely and becomes coarse with slower cooling. Mechanical properties correlate with observed microstructure and transformation behaviour. Results suggest high strength and good toughness for cooling rates between 800 and 500uC of about 3-13 s. A fine microstructure will then form with varying proportions of martensite, lower bainite, coalesced bainite and fine upper bainite.

Neural network predictions suggested that the strength of a high strength steel weld metal with 7 wt-% nickel and 0 . 5 wt-% manganese could be increased significantly at moderate expense to impact toughness by additions of carbon. Based on this, three experimental weld metals were produced with carbon contents between 0 . 03 and 0 . 11 wt-%. Mechanical test results were in agreement with predictions. At low carbon content the microstructure was largely bainitic in dendrite core regions whereas martensite was found at interdendritic regions. From microstructural studies and dilatometry experiments it was found that carbon stabilised austenite to lower transformation temperatures and that the microstructure became more martensitic in nature. Effects on strength and impact toughness were explainable in terms of a refinement of the microstructure and tempering behaviour.

Two experimental high strength steel weld metals were produced with 7 wt-% nickel and either 2 or 0 . 5 wt-% manganese. Neural network predictions that it is advantageous to reduce the manganese concentration in high nickel alloys have been confirmed, with impact energy increasing from 32 to 113 J at -40uC. High resolution microstructural investigations showed that both weld metals contained mainly martensite at interdendritic regions and predominantly bainite at dendrite core regions, as a consequence of manganese and nickel segregation. In the high manganese weld metal significant amounts of coarse grained coalesced bainite formed whereas mainly upper bainite was seen with 0 . 5 wt-% manganese. Reducing manganese content increased the transformation temperature, promoting fine upper bainite at the expense of coarse coalesced bainite. Increased toughness was attributed to the finer grain size of bainite constituents and a more effectively tempered microstructure.