Volume 51, Issue 2

In this study, quantitative microstructural investigations were performed to understand the influence of the processing route on the grain and particle structures in an Al-Mg alloy (AA5754). The microstructures of two different batches of 5754-O sheets of the same composition (one produced by direct-chill casting (DC) and the other by continuous casting (CC)) were investigated using optical, scanning and transmission electron microscopy. Several characteristic microstructural features were linked to the processing route, especially the banding of the Fe-rich constituent particles along the rolling direction (RD) combined with a through-thickness variation in grain size alloys produced by CC, compared to a random particle distribution of relatively coarser sizes and a roughly uniform through-thickness grain size distribution in the alloys produced by DC. The study also assessed the significance of the characteristic microstructural features associated with DC and CC (e. g. particle size banding and grain size variation) on the identification the processing route, highlighting the features that represent inconclusive evidence for a certain route.

TiC coatings on AISI D3 cold-work tool steel were carried out by pack method thermo-reactive diffusion process (TRD) for 2 and 4 h at 950, 1 000, 1 050 and 1 100 °C, respectively. The carbide layers were evaluated based on microstructure, thickness, hardness, energy dispersive X-ray facility and X-ray diffraction analysis. Titanium carbide layer thickness on the coated specimens ranged from 6 to 23 μm, depending on treatment time and temperature. Growth kinetics of the carbide layers were analyzed measuring the depth of carbide layer as a function of temperature and time. The activation energy was estimated to be 249.42 kJ/mol. The micro-hardness value of the coating layer was obtained to be 2 470 HV in maximum.

In the present paper, we selected or designed several etchants to characterize the solidification modes, the distribution of micro-segregation and the grain morphology of cast Fe-Mn-Si-Cr-Ni SMAs solidifying as A, AF, FA and F modes based on the principle of metallography. The results showed that a tint etchant based on 0.5 g K 2 S 2 O 5 , 20 g NH 4 HF 2 and 100 ml H 2 O can only characterize the grain morphology of cast Fe-Mn-Si-Cr-Ni SMAs solidifying as F and FA modes and can reveal the typical microstructures of FA, AF and A modes. An ordinary etchant (1 ml HF, 15 ml H 2 O 2 , 1 g C 2 H 2 O4 and 15 ml H 2 O) can only reveal the typical microstructures of F mode. As a result, the solidification modes of cast Fe-Mn-Si-Cr-Ni SMAs are determined by using both tint etchants together. Another tint etchant (20 g K 2 S 2 O 5 , 1 g NH 4 HF 2 and 100 ml H 2 O) can qualitatively characterize the distribution of micro-segregation in cast Fe-Mn-Si-Cr-Ni SMAs with four solidification modes.

Focused on tissue interactions and the properties of the materials themselves, the causes of dental implant failure can be analysed successfully using methods developed within materials science. This will be exemplified by three failing implants. The implants represent a broad range of materials (titanium, PEEK, zirconium dioxide) and geometries (screw, cylindrical, disc). Materials and methods: Following appropriate specimen collection and preparation, EDX, ESEM, light microscopy and ultrasound examinations were performed. Since only the titanium implant exhibited osseointegration, the implant-bone interface of this implant was additionally analysed by FIB-TEM. Results: The absence of bone tissue residue on the zirconium dioxide and PEEK implants was confirmed by all imaging methods. Complete osseointegration is demonstrable only for a complete fragment of the titanium implant resected from the jaw bone, with a bone-to-metal contact of 82.5 %. Conclusion: A bioactive interaction with the target tissues was found only for the titanium implant. The loss of the titanium implant examined was due to a material failure. High-frequency ultrasonic microscopy has proven a suitable tool for the assessment of osseointegration. A reduced sample preparation effort and an ability to use ultrasound in situ would suggest that ultrasonic microscopy technology is a suitable technology for failure analysis.