Comparison of Aerosol Pt, Au and Ag Nanoparticles Agglomerates Laser Sintering

In this paper, we investigated the interaction of nanosecond pulsed-periodic infrared (IR) laser radiation at a 50 and 500 Hz repetition rate with aerosol platinum (Pt) and silver (Ag) nanoparticles agglomerates obtained in a spark discharge. Results showed the complete transformation of Pt dendrite-like agglomerates with sizes of 300 nm into individual spherical nanoparticles directly in a gas flow under 1053 nm laser pulses with energy density 3.5 mJ/cm2. Notably, the critical energy density required for this process depended on the size distribution and extinction of agglomerates nanoparticles. Based on the extinction cross-section spectra results, Ag nanoparticles exhibit a weaker extinction in the IR region in contrast to Pt, so they were not completely modified even under the pulses with energy density up to 12.7 mJ/cm2. The obtained results for Ag and Pt laser sintering were compared with corresponding modification of gold (Au) nanoparticles studied in our previous work. Here we considered the sintering mechanisms for Ag, Pt and Au nanoparticles agglomerates in the aerosol phase and proposed the model of their laser sintering based on one-stage for Pt agglomerates and two-stage shrinkage processes for Au and Ag agglomerates.

Effects of Composite Sintering Additives: Al(OH)3+Y2O3+CaF2 on the Performance of Porous Mullite Oxide-Bonded SiC Ceramics

A composite sintering additive system: Al(OH)3+Y2O3+CaF2 was proposed for porous mullite oxide-bonded SiC ceramics. Small variations of sintering additives have significant influences on the phase composition, pore shape/size, density and flexural strength. Samples sintered at 1550 ℃ for 4 h in the air atmosphere realized both good mullite densification and no detectable cristobalite phase, which was difficult to be achieved at the same time. Besides, the composite sintering additive system also promoted the formation of columnar shape mullite, which acts as a reinforcement. Flexural strength as high as 108 MPa was achieved at an apparent porosity of 40.3 vol%, which is higher than that sintered by SPS technique. Moreover, those additives also act as pore formers determining the shape and size of pores. Around 8.9 µm strip-like, 11.8 µm continuous channel-like and 4.1 µm irregular pores were obtained for Al(OH)3, Al(OH)3-Y2O3 and Al(OH)3-Y2O3-CaF2 added samples, respectively. Corresponding phase evolution, sintering mechanisms and pore formation models were established. This work provides a simple way to modify the phase, pore size/shape, and strength of mullite oxide-bonded porous SiC ceramics by properly selecting sintering additives without any additional pore formers.

Effect of Sintering Mechanisms On The Mechanical Behaviour of SiC And Kaoline Reinforced Hybrid Aluminium Metal Matrix Composite Fabricated Through Powder Metallurgy Technique

Hybrid metal matrix composites with naturally available and low-cost reinforcements made tremendous demand in the automobile industry to fabricate parts like Pistons, Automobile body and brake discs because of the superior properties of HMMC compared to monolithic Aluminium. Present work focusses on the fabrication of Al-10% SiC-4% Kaoline HMMC by using conventional sintering, Microwave sintering and Spark Plasma Sintering (SPS) techniques. To reveal the phase identification and the distribution of reinforcements, Fabricated composites were investigated by using XRD, SEM integrated with an EDS analyser. Tensile, Compression and hardness tests were performed as per ASTM standards to study the effect of sintering mechanisms on the fabricated HMMC specimens. Results reveal that an enhancement of 13.3 % in U.T.S and 11.7 % Compression strength was observed in the Spark Plasma Sintered HMMC when compared to conventional sintered composite specimens because of lesser sintering temperature, time and the absence of intermetallic compounds in the Spark Plasma Sintering process. The formation of the Al2Cu intermetallic compound was identified in the XRD pattern of conventionally sintered Al-10% SiC-4% Kaoline HMMC sample due to the high sintering time and temperature which leads to inadequate mechanical properties. The fractured surface of tensile specimens reveals the presence of cleavages on the conventionally sintered HMMC which conforms the brittle fracture, and the existence of dimples on the Microwave sintered and Spark Plasma Sintered samples which signify that the ductile mode of failure in HMMC samples. Out of the three sintering techniques, Spark Plasma Sintering exhibits superior mechanical properties and lesser porosity levels.

Microstructure and Residual Stress Evolution of Laser Powder Bed Fused Inconel 718 under Heat Treatments

The current work aimed to study the influence of various heat treatments on the microstructure, hardness, and residual stresses of Inconel 718 processed by laser powder bed fusion process. The reduction in residual stresses is crucial to avoid the deformation of the component during its removal from the building platform. Among the different heat treatments, 800 °C kept almost unaltered the original microstructure, reducing the residual stresses. Heat treatments at 900, 980, and 1065 °C gradually triggered the melt pool and dendritic structures dissolution, drastically reducing the residual stresses. Heat treatments at 900 and 980 °C involved the formation of δ phases, whereas 1065 °C generated carbides. These heat treatments were also performed on components with narrow internal channels revealing that heat treatments up to 900 °C did not trigger sintering mechanisms allowing to remove the powder from the inner channels.