The increasing environmental concern has reawakened an interest in materials based on renewable resources as replacement for petroleum-based materials. The main objective of this thesis was to explore plant proteins, more specifically wheat gluten, as a binder in wood adhesives intended for typical solid wood applications such as furniture and flooring. Alkaline and acidic dispersions of wheat gluten were used as wood adhesives to bond together beech wood substrates. Soy protein isolate was used as a reference. The tensile shear strengths of the substrates were measured for comparison of bond strength and resistance to cold water. AFM in colloidal probe mode was used to investigate nanoscale adhesion between cellulose and protein films. Wheat gluten was divided into the two protein classes; glutenins and gliadins, and their adhesive performance was compared with that of wheat gluten. Heat treatment and mild hydrolysis were investigated as means for improving bonding performance of wheat gluten. The treated wheat gluten samples were analysed by SE-HPLC and 13C-NMR to correlate molecular size distribution and structural changes with bonding performance. Soy protein isolate is superior to wheat gluten, especially in regards to water resistance. However, the bond strength of wheat gluten is improved when starved bond lines are avoided. The AFM analysis reveals higher interfacial adhesion between soy protein isolate and cellulose than between wheat gluten and cellulose. These results partly explain some of the differences in bonding performance between the plant proteins. Soy protein isolate contains more polar amino acid residues than wheat gluten and possibly interacts more strongly with cellulose. Furthermore, the bond performances of wheat gluten and glutenin are similar, while that of gliadin is inferior to the others, especially regarding water resistance. The extent of penetration of the dispersions into the wood material has a large impact on the results. The bonding performance of gliadin is similar to the others when over-penetration of the dispersion into the wood material is avoided. Moreover, the bond strength of the wheat gluten samples heated at 90°C was in general improved compared to that of wheat gluten. A small improvement was also obtained for some of the hydrolyzed wheat gluten samples (degree of hydrolysis: 0-0.6 %). The improvements in bonding performance for the heat treated samples are due to polymerization, while the improvements for the hydrolyzed samples are due to denaturation. The 13C-NMR analysis of the treated samples confirms some degree of denaturation. / QC 20120514

Aluminum alloys are having more attention due to their high specific stiffness and processing advantages. 7075 aluminum alloy is a wrought composition aluminum alloy in the Al-Zn-Mg-Cu series. Due to the significant addition of these alloying elements, 7075 has higher strength compared to all other aluminum alloys and effective precipitation hardenability characteristic. On the other hand, aluminum alloys have some drawbacks, which hinder the widespread application of them. One of the most commonly encountered defects in aluminum alloys is the hydrogen porosity. Additionally, in case of 7075, another problem is the lack of fluidity. Magnesium addition is thought to be effective in compensating this deficiency. Accordingly, in this study, die cast 7075 aluminum alloy samples with hydrogen porosity and additional magnesium content were investigated. The aim was to determine the relationship between hydrogen content and hydrogen porosity, and the effects of hydrogen porosity, additional magnesium and T6 heat treatment on ultimate tensile and flexural strength properties of pressure die cast 7075 aluminum alloy. 7075 aluminum alloy returns were supplied from a local pressure die casting company. After spectral analysis, pressure die casting was conducted at two stages. In the first stage, 7075 aluminum alloy with an increase in magnesium concentration was melted and secondly 7075 aluminum alloy was cast directly without any alloying addition. While making those castings, hydrogen content was measured continuously before each casting operation. As a final operation T6 heat treatment is carried out for certain samples. Finally, in order to accomplish our aim, mechanical and microstructural examination tests were conducted.

No description available.

No description available.

In this research, controlled Waspaloy microstructures were produced with the objective of studying microstructural evolution in this alloy via electrically-based ac/dc non-destructive techniques. Correlations were developed between electrical measurements and alternate characterization techniques such as Ultra Small Angle X-ray Scattering (USAXS), Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) to gain a complete understanding of the microstructural transformations and the associated mechanisms. Three different sets of controlled microstructures were produced in this research. In Set I microstructures, matrix (gamma) grain sizes of 13, 52 and 89 micrometers were obtained after solution-treatments at 1045 and 176;C, 1090 and 176;C and 1145 and 176;C respectively. A vacancy stabilization treatment at 1045 and 176;C followed after which, the specimens were aged at 800 and 176;C for times ranging from 0.1 hrs to 100 hrs to vary the gamma prime precipitate size distribution. In Sets II and III, the solution-treatment was only conducted at 1145 and 176;C, with the stabilization treatment conducted only in Set II. Subsequently, aging experiments were conducted at 725 and 176;C (or 700 and 176;C in Set II), 800 and 176;C and 875 and 176;C for times up to 100 hrs. DC four-point probe resistivity of specimens increased to a maximum upon initial aging from the solution-treated condition and showed a decreasing trend thereafter with successive aging. This, in addition to complementary evidence from SEM and USAXS, led to the conclusion that gamma prime nucleation-growth was complete by the time the resistivity maximum was observed. Resistivity variations that ensued upon successive aging after the maximum were attributed to microstructural/compositional changes due to gamma prime coarsening. The height of the maximum decreased drastically with increase in aging temperature from 725 and 176;C to 800 and 176;C, while the resistivity did not increase from the solution-treated condition upon aging at 875 and 176; C. Coarsening studies based on USAXS analysis indicated an LSW type volume diffusion mechanism of coarsening in Waspaloy, with an average coarsening rate constant of 3.25x10-29 [m3/sec] for Set I specimens aged at 800 and 176;C. Analytical and Finite Element (FE) models of two-probe impedance and dc four-point probe resistivity methods were developed to gain insight into the measured response and the accurate determination of material properties. AFM-based localized electrical examination of sub-grain Waspaloy microstructures was successfully conducted using electrostatic force microscopy (EFM), scanning Kelvin probe microscopy (SKPM) and current-AFM (I-AFM) electrical modes. I-AFM experiments revealed that the conductivity of the gamma prime phase was lower than that of the gamma phase.

Microstructural and mechanical characterizations of heat treatable Al-Mg-Si-Cu based wrought aluminum alloys have been studied. The aim of this work was to produce fine grained, high strength alloy by adjusting processing conditions: deformation, solutionizing and aging. First, primary characterization was carried out via SEM-EDS analyses and tensile tests. Then an extensive experimental study has been carried out on two sets of samples. The first set has been studied to determine the ideal conditions for solutionizing and aging processes by analyzing the variation of hardness with different solutionizing and aging time and temperature. The second set, have first been mechanically deformed by swaging at four different deformations and four different temperatures, then heat treated. The hardness measurements have been carried out before and after solutionizing and also after aging. Finally, recrystallization behavior has been investigated by measuring grain size before and after solutionizing treatment using image analyzer software. The initial characterizations showed that Mg2Si and complex iron, manganese bearing intermetallics were the primary particles observed in the &amp / #945 / -Al matrix. Nearly 140HB hardness could be obtained with solutionizing at 530&deg / C and aging at 175&deg / C for 8 hours which was determined as the optimum treatment for obtaining peak hardness. When shaping (deformation) was concerned / strength loss was the overall outcome of any hot or cold deformation before solutionizing / which was most probably due to the destruction of the initial microstructure. Improvement in the percent elongation was the promising aspect of this application. Strength loss was increased for samples deformed at higher temperatures and higher reductions.

<p>Wood plastic composite (WPC) materials have seen a continuous market growth worldwide in the last decade. So-called extruded WPC profiles are today mainly used in outdoor applications, e.g. decking, railing and fencing. In outdoor conditions, moisture sorption in the wood component combined with temperature induced movements of the polymer matrix causes deformations of such composites. On the macroscopic scale this may lead to unacceptable warp, cup and bow of the WPC products, but on a microscopic scale, the movements will cause interfacial cracks between the particles and the matrix, resulting in little or no ability to transfer and re-distribute loads throughout the material. Moisture within the composite will also allow fungi and micro organisms to attack the wood particles.</p><p>The conceptual idea of this work is to use a chemically modified wood component in WPCs to enhance their long term performance. These chemically modified wood particles exhibit reduced susceptibility to moisture, resulting in better dimensional stability and a higher resistance to biological degradation as compared to that of unmodified wood. The objective of this thesis is to study the effects of using modified wood in WPCs on their moisture sorption behaviour, micromorphology and microbiological durability. The modification methods used were acetylation, heat treatment and furfurylation.</p><p>Equilibrium moisture content (EMC) and sorption behaviour of WPCs were determined by water vapour sorption experiments. The use of thin sections of the composites enabled EMC to be reached within a comparably short time span. The micromorphology was studied by LV-SEM (low vacuum-scanning electron microscope) using a specially designed sample preparation technique based on UV laser. The biological durability was evaluated by laboratory fungal test methods.</p><p>The moisture sorption experiments showed lower moisture levels for all the composites when modified wood particles were used. This was also reflected in the micromorphological studies where pronounced wood-plastic interfacial cracks were formed due to moisture movement in the composites with unmodified wood particles. The sample preparation technique by UV laser proved to be a powerful tool for preparing surfaces for micromorphological studies without adding mechanical defects caused by the sample preparation technique itself. Results from the durability test showed that WPCs with modified wood particles are highly resistant to decay by fungi.</p>

Precipitation strengthened nickel-base superalloys, such as IN 738, are very difficult to weld by fusion welding techniques due to their high susceptibility to heat-affected zone (HAZ) intergranular liquation cracking. An improvement in weldability could be realized by the deployment of innovative welding processes and/or the modification of the materials’ microstructural characteristics. Laser-arc hybrid welding is a relatively new welding process that appears to possess great potentials for joining the difficult-to-weld nickel-base superalloys. The research described in this Ph.D. dissertation was initiated to perform a systematic and comprehensive study of the cracking susceptibility of nickel-base IN 738 superalloy welds made by laser-arc hybrid welding process, and how to minimize it by using a combination of pre-weld microstructural modification and the application of various welding filler alloys. Laser-arc hybrid welding produced a desirable weld geometry in IN 738 Superalloy. Cracking did not occur exclusively in the fusion zone. Analysis of the fusion zone material using EPMA, SEM, TEM and EBSD revealed elemental partitioning pattern, the presence of secondary solidification reaction constituents and the grain structure of the fusion zone. Non-equilibrium liquation of various second phases that were present in the alloy prior to welding contributed to intergranular liquation in the HAZ that consequently resulted in extensive HAZ intergranular cracking. A very significant reduction in HAZ intergranular liquation cracking was achieved by the use of an industrially deployable and effective pre-weld thermal processing procedure developed during this research work. This novel procedure, designated as FUMT, was developed on the basis of the control of both boride formation and intergranular boron segregation in the pre-weld material. Propensity for HAZ intergranular liquation cracking in the weldments was also observed to vary depending on the Al+Ti+Nb+Ta concentration of the weld metal produced by different filler alloys, which can be attributed to variation in the extent of precipitation hardening in the weld metals. The newly developed FUMT treatment procedure, coupled with the selection of an appropriate type of filler alloy, is effective in reducing HAZ intergranular cracking both during laser-arc hybrid welding and during post-weld heat treatment (PWHT) of the laser-arc hybrid welded IN 738 superalloy.

Precipitation strengthened nickel-base superalloys, such as IN 738, are very difficult to weld by fusion welding techniques due to their high susceptibility to heat-affected zone (HAZ) intergranular liquation cracking. An improvement in weldability could be realized by the deployment of innovative welding processes and/or the modification of the materials’ microstructural characteristics. Laser-arc hybrid welding is a relatively new welding process that appears to possess great potentials for joining the difficult-to-weld nickel-base superalloys. The research described in this Ph.D. dissertation was initiated to perform a systematic and comprehensive study of the cracking susceptibility of nickel-base IN 738 superalloy welds made by laser-arc hybrid welding process, and how to minimize it by using a combination of pre-weld microstructural modification and the application of various welding filler alloys. Laser-arc hybrid welding produced a desirable weld geometry in IN 738 Superalloy. Cracking did not occur exclusively in the fusion zone. Analysis of the fusion zone material using EPMA, SEM, TEM and EBSD revealed elemental partitioning pattern, the presence of secondary solidification reaction constituents and the grain structure of the fusion zone. Non-equilibrium liquation of various second phases that were present in the alloy prior to welding contributed to intergranular liquation in the HAZ that consequently resulted in extensive HAZ intergranular cracking. A very significant reduction in HAZ intergranular liquation cracking was achieved by the use of an industrially deployable and effective pre-weld thermal processing procedure developed during this research work. This novel procedure, designated as FUMT, was developed on the basis of the control of both boride formation and intergranular boron segregation in the pre-weld material. Propensity for HAZ intergranular liquation cracking in the weldments was also observed to vary depending on the Al+Ti+Nb+Ta concentration of the weld metal produced by different filler alloys, which can be attributed to variation in the extent of precipitation hardening in the weld metals. The newly developed FUMT treatment procedure, coupled with the selection of an appropriate type of filler alloy, is effective in reducing HAZ intergranular cracking both during laser-arc hybrid welding and during post-weld heat treatment (PWHT) of the laser-arc hybrid welded IN 738 superalloy.

High strain rate plastic deformation of metals results in the formation of localized zones of severe shear strain known as adiabatic shear bands (ASBs), which are a precursor to shear failure. The formation of ASBs in a high-strength low alloy steel, namely AISI 4340, was examined based on prior heat treatments (using different austenization and tempering temperatures), testing temperatures, and impact strain rates in order to map out grain size and grain deformation behaviour during the formation of ASBs. In the current experimental investigation, ASB formation was shown to be a microstructural phenomenon which depends on microstructural properties such as grain size, shape, orientation, and distribution of phases and hard particles—all controlled by the heat treatment process. Each grain is unique and its material properties are heterogeneous (based on its size, shape, and the complexity of the microstructure within the grain). Using measurements of grain size at various heat treatments as well as dynamic stress-strain data, a finite element model was developed using Matlab and explicit dynamic software LSDYNA to simulate the microstructural deformation of grains during the formation of ASBs. The model simulates the geometrical grain microstructure of steel in 2D using the Voronoi Tessellation algorithm and takes into account grain size, shape, orientation, and microstructural material property inhomogeneity between the grains and grain boundaries. The model takes advantage of the Smooth Particle Hydrodynamics (SPH) meshless method to simulate highly localized deformation as well as the Johnson-Cook Plasticity material model for defining the behavior of the steel at various heat treatments under high strain rate deformation.The Grain Model provides a superior representation of the kinematics of ASB formation on the microstructural level, based on grain size, shape and orientation. It is able to simulate the microstructural mechanism of ASB formation and grain refinement in AISI 4340 steel, more accurately and realistically than traditional macroscopic models, for a wide range of heat treatment and testing conditions.