ABSTRACT
A Ni2MnSn Heusler alloy was obtained as a single B2 phase after 12 h of mechanical milling. The influence of prolonged milling on the phase stability was analysed for milling times up to 50 h, related to mean crystallite size, lattice strain, and electrical resistivity. The nature of the powders in the milled range was found to be nanocrystalline, with a mean crystallite size of about 33 ± 2 nm. An evaluation of the internal stresses induced by milling was performed, a linear behaviour was found, and a coefficient of the internal stress increase with milling time was proposed. Particle size distributions of milled samples were analysed, and the morphology of the powders was visualised by scanning electron microscopy. The elemental distribution of milled samples was quantified by energy-dispersive X-ray spectroscopy. Electrical resistivity measurements were performed on compacted samples, and their behaviour with milling time was analysed.
ABSTRACT
The damage due to embrittlement of the sintering furnace belt and its replacement after a certain time of use represents a problem for the manufacturers of sintered parts. Finding out the reason for the damage could help to increase the duration of its operation. This research aimed to investigate the causes of embrittlement, considering both the temperatures and atmosphere of the sintering furnace to which the furnace belt is exposed during its operation. The furnace belt was made of AISI 314 stainless steel. Optical microscopy, scanning electron microscopy, combined with energy-dispersive X-ray analysis, X-ray diffraction and the Vickers hardness tests were used to analyze the microstructural, structural, compositional and hardness changes of the belt used for 45 weeks. Cr and Mn carbides, the oxides of Fe, Cr, Mn and Si were found to form at the edge of the furnace belt. The grains grew after 45 weeks of use, approximately 10 times, due to thermal cycles in an endothermic gas atmosphere to which the belt was exposed. Also, the hardness increased from 226 to 338 HV0.05, due to the formation of carbide and oxide-type compounds. All these results represent a starting point in optimizing the lifetime of the sintering furnace belt.
ABSTRACT
This paper presents the usage of spark plasma sintering (SPS) as a method to obtain aluminum-expanded perlite syntactic foams with high porosity. In the test samples, fine aluminum powder with flaky shape particles was used as matrix material and natural, inorganic, granular, expanded perlite was used as a space holder to ensure high porosity (35−57%) and uniform structure. SPS was used to consolidate the specimens. The structures were characterized by scanning electron microscopy and compression tests. Energy absorption (W~7.49 MJ/m3) and energy absorption efficiency (EW < 90%) were also determined.