This paper aims to provide a review on the process of additive manufacturing of ceramic materials, focusing on partial and full melting of ceramic powder by a high-energy…
This paper aims to provide a review on the process of additive manufacturing of ceramic materials, focusing on partial and full melting of ceramic powder by a high-energy laser beam without the use of binders.
Selective laser sintering or melting (SLS/SLM) techniques are first introduced, followed by analysis of results from silica (SiO2), zirconia (ZrO2) and ceramic-reinforced metal matrix composites processed by direct laser sintering and melting.
At the current state of technology, it is still a challenge to fabricate dense ceramic components directly using SLS/SLM. Critical challenges encountered during direct laser melting of ceramic will be discussed, including deposition of ceramic powder layer, interaction between laser and powder particles, dynamic melting and consolidation mechanism of the process and the presence of residual stresses in ceramics processed via SLS/SLM.
Despite the challenges, SLS/SLM still has the potential in fabrication of ceramics. Additional research is needed to understand and establish the optimal interaction between the laser beam and ceramic powder bed for full density part fabrication. Looking into the future, other melting-based techniques for ceramic and composites are presented, along with their potential applications.
– An engine component made from 1Cr18Ni9Ti alloy to be used underwater was the subject of the present research investigation.
An engine component made from 1Cr18Ni9Ti alloy to be used underwater was the subject of the present research investigation.
A stereomicroscope, a metallurgical microscope, a microhardness tester and an electron energy dispersion spectroscope were used to observe cross-sections of the alloy’s microstructure at different locations, as well as its overall corrosion behavior.
The corrosion of the 1Cr18Ni9Ti alloy, attributed to welding, cold processing and plastic deformation processes, was investigated together with an analysis of the chemical composition of the corrosion products and microsclerometry of the cross-sections. It was revealed that defects such as shrinkage cavities and porosity, often were observed to occur in the welding fusion zone. During cold processing treatments, work hardening was induced in the surface layer. Corrosion products consisted of oxides, chlorides and sulfides, with oxides as the dominant component. The high chromium content of d-ferrite had resulted in chromium depletion in nearby phase boundaries, which had led to oxidation and corrosion at these boundaries. As the electrode potential of d-ferrite is different to that of austenite, it is possible for a galvanic couple to develop between the two phases, leading to differential rates of corrosion attack.
Methods are proposed to improve corrosion resistance by improving the quality of the surface overlaying processes and by adopting special surface treatment techniques.