Effect of chemical composition and T6 heat treatment on the mechanical properties and fracture behaviour of Al-Si alloys for IC engine components

Microstructural examinations of Al-Si alloys intended to manufacture IC engine components revealed a complex phase composition in all samples. Polyhedral crystals of primary silicon were detected in Al-12.5Si alloy, besides the ?-Al phase, eutectic silicon, and several intermetallic phases, identified in the cast samples of both alloys. Better tensile properties were found for samples of Al-11Si. Predominantly intercrystalline fracture with features of ductile failure was observed in both alloys. In as-cast specimens of Al-11Si alloy, the cracks were formed by the decohesion mechanism between the particles of the intermetallic phase AlCuFeNi and ?-Al phase. The microcracks initiated on the interface were spread along the branches of ?-Al15(Fe,Mn,Cu)3Si2 particles. After T6 treatment of Al-11Si alloy, almost half the intermetallics quantity presented Al3Ni phase, while the iron-based phases were observed in a small amount. Spheroidized eutectic silicon, less portion of Al5Cu2Mg8Si6, and a more considerable quantity of Al3(Fe,Mn,Cu,Ni,Co) were detected for T6 specimens of Al-12.5Si alloy. The rounded crystals of eutectic silicon contributed to the improvement of their tensile properties. Larger and deeper dimples of mostly polygonal shapes were observed in the samples of Al-11Si alloy after T6 treatment. The microcracks have occurred at the boundary of the intermetallic phase/?-Al solid solution.

OXYGEN INFLUENCE ON THE PHASE COMPOSITION AND ELECTRICAL PROPERTIES OF SIPOS FILMS

The use of oxygen-doped semi-insulating silicon films of the SIPOS type as passivation coatings for semiconductor devices and IC makes it possible to increase the breakdown voltage of highvoltage devices. The aim of this work is to establish the influence of the oxygen content on the phase composition of SIPOS films and their electrophysical properties. The results of comprehensive studies show that SIPOS films at different values of γ have a complex phase composition of nanocomposites based on amorphous silicon containing silicon nanocrystals and silicon suboxides with a low oxidation state, such as SiO0.47, while SiO2 dioxide is not formed even at large values of γ.

Redox-Promoted Tailoring of the High-Temperature Electrical Performance in Ca3Co4O9 Thermoelectric Materials by Metallic Cobalt Addition

This paper reports a novel composite-based processing route for improving the electrical performance of Ca3Co4O9 thermoelectric (TE) ceramics. The approach involves the addition of metallic Co, acting as a pore filler on oxidation, and considers two simple sintering schemes. The (1-x)Ca3Co4O9/xCo composites (x = 0%, 3%, 6% and 9% vol.) have been prepared through a modified Pechini method, followed by one- and two-stage sintering, to produce low-density (one-stage, 1ST) and high-density (two-stage, 2ST) ceramic samples. Their high-temperature TE properties, namely the electrical conductivity (σ), Seebeck coefficient (α) and power factor (PF), were investigated between 475 and 975 K, in air flow, and related to their respective phase composition, morphology and microstructure. For the 1ST case, the porous samples (56%–61% of ρth) reached maximum PF values of around 210 and 140 μWm−1·K−2 for the 3% and 6% vol. Co-added samples, respectively, being around two and 1.3 times higher than those of the pure Ca3Co4O9 matrix. Although 2ST sintering resulted in rather dense samples (80% of ρth), the efficiency of the proposed approach, in this case, was limited by the complex phase composition of the corresponding ceramics, impeding the electronic transport and resulting in an electrical performance below that measured for the Ca3Co4O9 matrix (224 μWm−1·K−2 at 975K).

Studies on Cementation of Tin on Copper and Tin Stripping from Copper Substrate

Cementation of tin on copper in acid chloride-thiourea solutions leads to the formation of porous layers with a thickness dependent on the immersion time. The process occurs via Sn(II)-Cu(I) mechanism. Chemical stripping of tin was carried out in alkaline and acid solutions in the presence of oxidizing agents. It resulted in the dissolution of metallic tin, but refractory Cu3Sn phase remained on the copper surface. Electrochemical tin stripping allows complete tin removal from the copper substrate, but porosity and complex phase composition of the tin coating do not allow monitoring the process in unambiguous way.

Crystallization behaviour of Li2O·Nb2O5·SiO2 glass containing TiO2

This paper deals with the crystallization of glass 30Li2O?15Nb2O5?50SiO2?5TiO2 (mol%). The crystallization behavior was studied under isothermal and non-isothermal conditions. XRD and SEM methods were employed for determination of phase composition and microstructure of crystallized glass. It was detected that this glass crystallizes by the surface crystallization mechanism. SEM micrographs of the crystallized samples revealed that the crystals grow in the form of dendrites. The glass-ceramics with complex phase composition was obtained. Three crystalline phases were detected where LiNbO3 has grown as primary phase and a secondary ones Li2Si2O5 and SiO2 appeared. The calculated average crystallite sizes are: 27 nm for LiNbO3 , 115 nm for Li2Si2O5 and 45 nm for SiO2 . From the experimental data an activation energy of crystals growth, calculated using the Kissinger relation, is Ea = 275 ?10 KJ / mol.

Nature of Formation of the Areas Having an Ultrafine Grain Structure in Al-Li-Mg System Alloys

The structure of Al-Li-Mg system alloy 1420, containing a small quantity of Sc, Zr, Ti was investigated in cast, homogenized, hot-pressed, quenched and aged conditions, using the methods of optical metallography, transmission electron microscopy and X-ray examination. An existence of areas, having fine grains (20-30 nm)- "Ultrafine Grain areas"(UFGA) was observed in all the investigated conditions. UFGA are located on the boundaries, sub boundaries and S1(Al2MgLi) phase particles. UFGA can also form near the particles of crystallization origin. These areas have a complex phase composition. Inside the UFGA the particles of S1(Al2MgLi) phase and also δnon-phase, investigated in [1] are always present whereas δ'(Al3Li) precipitations are absent. These areas are formed during crystallization and hot deformation. Their composition changes during the treatment. The nature of these changes is considered.