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A Rietveld method is described which extracts information on crystal structure, texture and microstructure directly from two-dimensional synchrotron diffraction images. This is advantageous over conventional texture analysis that relies on individual diffraction peaks, particularly for low-symmetry materials with many overlapping peaks and images with a poor peak-to-background ratio. The method is applied to two mineralized biological samples with hydroxylapatite fabrics: an ossified pachycephalosaurid dinosaur tendon and an Atlantic salmon scale. Both are measured using monochromatic synchrotron X-rays. The dinosaur tendon has very strongly oriented crystals with c-axes parallel to the tendon direction. The salmon scale displays a weak texture.

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Selective laser melting (SLM) is a rapid prototyping technique based on melting and solidification of powder layers to build up a 3-D solid body. [1][2][3] It was developed as a prototyping technology, but is attracting ever-increasing interest as a rapid manufacturing technology for the production, for instance, of orthopedic prostheses made of titanium and cobalt alloys [4,5] and die inserts made of low alloys and maraging steels for the plastics industry. [6,7] Because of the large solidification undercooling, SLM results in the formation of either very fine or metastable microstructures, which sometimes do not find a correspondence in the alternative technologies and in the international standards, as in the case of titanium alloys. [8] An in-depth investigation on the effect of the microstructure on mechanical properties is necessary to evaluate whether or not such a peculiar microstructure is acceptable for practical applications.SLM is used for the production of surgical tools, as well. In this case, a stainless steel combining mechanical strength, wear resistance and corrosion resistance is the best choice. This requirement is satisfied by the precipitation-hardening (PH) stainless steels. Among them, the 17-4 PH grade is a high-chromium steel with a martensitic microstructure (resulting from the transformation of austenite on cooling), which has to be heat treated (solution annealing and aging) to promote the precipitation of Cu phases. [9] In this material, the large solidification undercooling may prevent the formation of martensite in the as-built material, leading to a metastable austenitic microstructure.Metastable austenite may transform into martensite on straining, resulting in the well-known transformation-induced plasticity (TRIP) phenomenon. TRIP is exploited in some steel grades, namely the low alloyed Si-Mn steels as well as the high alloyed Mn-Si-Al steels, to improve their plastic ductility in cold forming. TRIP is also displayed by austenitic stainless steels. Its occurrence depends on the stacking fault energy (SFE) of austenite: [10] on decreasing SFE, deformation occurs by perfect and partial dislocation gliding, by twinning and then by martensitic transformation. With a SFE below 15-20 mJ m À2 , austenite transforms to e and a' martensite, resulting in an increase in strain hardenability and, in turn, ductility.An increase in toughness due to the presence of retained austenite in a 17-4 PH stainless steel was reported by Nakagawa and Miyazaki; [11] up to 30% austenite was stabilized in the microstructure by a special heat treatment. However, a mostly austenitic 17-4 PH stainless steels has never been investigated.In this paper, a study on the microstructure of a 17-4 PH stainless steels, produced by SLM, and on its effect on the tensile properties is presented. The as-built microstructure contains a large amount of metastable austenite. Tensile tests show a large plastic ductility coupled to significant strain hardenability, resulting in a high tensile strength around 1 GPa. The trans...

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The first evidence is provided for the existence of a tetragonal or slightly orthorhombic unit cell of bainitic ferrite. It supports the hypothesis that the excess carbon that persists in the ferrite, which is in contact with austenite, is a consequence of an increased solubility due to the change in symmetry from the conventional cubic unit cell. The deviations from the cubic cell are maintained to elevated temperatures, as expected from an increased solubility of carbon in the ferrite.