Journal of advanced materials and processing
Volume:1 Issue: 3, Summer 2013

Inorganic polymers were synthesized from dehydroxylated aluminosilicate clay (metakaolinite) condensed with sodium silicate in a highly alkaline environment. The thermal treatment of aluminosilicate materials causes changes in their structure with an increase in the amorphous phase. For that kind of structural change XRD analysis is not appropriate, so those changes are currently assessed by infrared emission spectra analysis (FTIR). The most characteristic FTIR band in the geopolymeric systems appears in the wavenumbers region 990-1090cm-1 and is attributed to the asymmetric stretching vibration of T-O-Si, where T denotes Si or Al. The shift of this peak towards lower wavenumbers indicates the dissolution of the amorphous aluminosilicate phase of the raw material and the formation of a new amorphous gel in which the backbone consists of polymeric chains with smaller length in relation to the ones of the raw material. The SEM result showed that geopolymer paste was formed from quartz remaining particles and gel. The remaining particle size was reduced by increase of the curing temperature and Na2O/SiO2 molar ratio. The results indicated that samples with adequate strength are created compact and crack-free areas.

The proportional relationships between the Charpy absorbed energy (CVN) and the KIC values have been established for a wide variety of steels. Several formulae have been proposed that predict KIC from CVN. The purpose of this study is to investigate, by means of compact testing fracture toughness specimens, the effective role of microstructure for estimation of the fracture toughness (KIC) of rotor steel using Charpy absorbed energy (CVN). To achieve this objective, a number of rotor steel samples were heat treated by step quenching procedure, and the fracture toughness and impact energy were measured. It was found that the calculated fracture toughness values, which were derived using a developed CVN-KIC relationship, disagreed with the experimental results.

Semisolid processing is one of the modern routes in sound and near net shape parts production. Preparation of semisolid slurry using a cooling slope is increasingly becoming popular, primarily because of its simplicity in design and ease of control of the process. In this research, the microstructures of Al6061 semisolid alloy cast via a miniature cooling slope were investigated. The properties of final microstructures such as sphericity depend on such casting factors as pouring rate, superheat, slope angle and slope length. In this work, the relationships between the process parameters and microstructural properties of semisolid castings were identified using a two level factorial design. The results showed that simultaneous increase or decrease in pouring rate and cooling slope length can result in the most proper microstructure. The optimum result was then successfully used for semisolid welding of the alloy.

Microstructural changes during laser welding and laser surface treatment has been regarded by many researchers. Most researches have focused on studying the effect of various process parameters on the size and microstructure of the heat affected zone. But some studies show that the initial microstructure of the base metal can also affect the heat affected zone dimensions and final microstructure. In this research, the effect of initial grain size on final microstructure of the heat affected zone in laser surface melting process has been studied. For this purpose we used phase field simulation technique. The results showed that the change in initial grain size can lead to a change in the size of the heat affected zone and grain topology in this area.

This work studied the effect of additions of carbon dioxide to argon shielding gas on the weld shape and microstructure of ST14 steel in pulsed Nd: YAG laser welding. By additions of carbon dioxide up to 15%,the weld area and depth/width ratio decreases while rising of carbon dioxide up to 25% causes increasing of weld area and depth/width ratio. It is observed that the weld metal microstructure is mainly constructed from polygonal ferrite under 0 to 15% CO2 additions to argon, but both polygonal and acicular ferrites are observed as the CO2 level of Ar+ CO2 mixtures increases from 15 to 25%. The shape and microstructure of pulsed Nd: YAG laser welds is believed to be closely related to laser absorption coefficient, laser energy absorption on the work-piece surface and formation of oxide layer on the work-piece surface.

Recently, geopolymer binders have been considered because of low cost, simple processes for synthesis and many raw materials in nature. Geopolymer with brittle nature does not have high strength and cannot be used alone for structural materials. Therefore, to use in different structures, the composite which is reinforced with fibers such as carbon, glass, basalt, etchasbeen used. In this research, influence of different parameters such as firing temperature and weight fraction of continuous basalt fiber on strength of lithium-based geopolmer composites reinforced by basalt fibers was studied. Firstly, raw materials for geopolymer preparation were calcined. Then, geopolymer matrix with specific molar ratio was made with three different weight percent of basalt fiber. The Molds were put in an oven and after that the composites were taken out of the molds. Then the samples were cured at three different temperatures. After heat treatment, C-MOR of composites was tested and flexural strength and fracture energy for different samples were calculated. The results showed that basalt fiber composites at 200˚C had high strength, but by increasing temperature the strength decreased. Also, Fracture energy of composites at 200˚C was higher than other temperatures.

Mechanical alloying is a powder metallurgy processing technique involving cold welding, fracturing, and rewelding of powder particles in a high-energy ball mill. In this work, NiFe-TiC composite powders were prepared by mechanical alloying process using planetary high-energy ball mill. The effect of TiC addition by weight percent on the NiFe solid solution formation, grain size, lattice parameter, internal strain and hardness of composite powders was investigated as a function of milling time, t, (in the 0-25 h range). Microstructural and phase characterizations investigationof the mechanically alloyed powders were carried out using X-ray diffractometer (XRD) and scanning electron microscope (SEM). The results showed that the brittle particles of TiC accelerate the milling process by increasing the matrix deformation and enhancing the welding and the fracture of particles. We also found that the NiFe solid solution formation occurred at earlier time of mechanical alloying with increasing the TiC content. Moreover, it was shown that with increasing the TiC by weight percent, smaller crystallite size and more hardness are obtained after mechanical alloying.