Proefschrift--Technische Hogeschool, Deltf. 1951. / "Stellingen": [3] p. inserted. eContent provider-neutral record in process. Description based on print version record. Bibliographical footnotes.

Proefschrift--Technische Hogeschool, Deltf. 1951. / "Stellingen": [3] p. inserted. Bibliographical footnotes. Also issued in print.

Thesis (M.S.)--University of Wisconsin--Madison, 1964. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 19.

Thesis (Ph. D.)--Worcester Polytechnic Institute. / Keywords: Microstructure; Elastic-Plastic Fracture Mechanics; Crack closure; A356; J-integral; Conventionally cast and SSM Al-Si-Mg alloys; Residual stress; Heat treatment; Fatigue crack growth mechanisms; Threshold stress intensity factor; Plastic zone; Paris law; Fracture toughness; Roughness. Includes bibliographical references.

Thesis (M.S.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Solute segregation in materials with grain boundaries (GBs) has emerged as a popular method to thermodynamically stabilize nanocrystalline structures. However, the impact of varied GB crystallographic character on solute segregation has never been thoroughly examined. This work examines Co solute segregation in a dataset of 7272 Al bicrystal GBs that span the 5D space of GB crystallographic character. Considerable attention is paid to verification of the calculations in the diverse and large set of GBs. In addition, the results of this work are favorably validated against similar bicrystal and polycrystal simulations. As with other work, we show that Co atoms exhibit strong segregation to sites in Al GBs and that segregation correlates strongly with GB energy and GB excess volume. Segregation varies smoothly in the 5D crystallographic space but has a complex landscape without an obvious functional form.

Crystallographic texture in polycrystalline materials are known to play an important role in tailoring suitable properties for various technological applications. In addition, the evolution of texture provides a profound basis to develop scientific understanding of physical processes occurring in the material during deformation and annealing. Between the two, the understanding of deformation texture is much broader. However, certain issues pertaining to the evolution of deformation texture evolution are yet to be explored or not uniquely agreed upon. A few notable examples are the effects of extreme grain sizes and strain rates. Moreover, most of the studies are pertaining to single phase metals and alloys. While many engineering alloys consist of two phase microstructures, the effect of second phase in the microstructure on the evolution of texture in the individual phases has not been studied in a comprehensive manner. The present thesis is an attempt to addresses these issues in a more generic manner. The studies have been specifically aimed at examining the aforesaid issues in the close packed Face Centre Cubic (FCC) and Hexagonal Close Packed (HCP) metals and alloys. In brief, this thesis addresses the following problems pertaining to deformation texture: (i) the effect of extreme grain sizes, (ii) the effect of extreme strain rates and (iii) the effect of a second ductile phase. Chapter 1 of the thesis gives a detailed survey of literature pertaining to the evolution of deformation textures in different metals and alloys, while chapter 2 includes the details of the experimental techniques and simulation procedures, which are mostly common for the entire work. The issue of grain size is addressed in chapter 3. In the present investigation, the evolution of deformation texture in nickel (FCC) and titanium (HCP) with the extreme grain sizes (nanometre and millimetre) has been studied. Nanocrystalline nickel with the grain size ~ 20 nm was obtained by pulse electro-deposition while the other extreme of the grain size in nickel was obtained by annealing of a cold rolled sheet at 1373 K. The rolling texture in nanocrystalline nickel had a higher volume fraction of Brass component than in nickel with normal grain size. These results have been explained on the basis of inhibition of cross slip in small grain sizes and the operation of planar slip. This has been validated by viscoplastic self-consistent simulations. The texture of coarse grain nickel samples (typified as oligocrystalline, owing to the lesser number of grains in the thickness direction) also had higher Brass component like the nanocrystalline sample. A detailed analysis was performed by examining misorientation development in the grain interior and in the vicinity of the grain boundaries. The similarity at the two extreme length scales has been explained on the basis of lower “Grain Boundary Affected Zone” at the extreme length scales. To examine the effect of grain size in the case of HCP materials, commercially pure titanium with ultra-fine (500 nm) and normal grain size (~50 μm), was investigated. A monotonic evolution of texture was observed in the former, which has been attributed to the absence of twinning, a situation that could arise due to the lack of coordinated movement of twinning partials in the sub-micron grain size regime. Thus, a reasonable understanding of the evolution of deformation texture in hitherto unexplored regime of grain sizes was developed for the two materials. The chapter 4 of the thesis is dedicated to the study of strain rate effects in both FCC and HCP materials. The issue of strain rate has been addressed by two ways: (a) deforming the materials at extreme strain rates, namely 10-3 s-1 to 10+3 s-1 under compression up to a reasonable strain, and (b) deforming the materials under torsion within a reasonable range of strain rates, but up to large strains. In this case, in addition to nickel, copper was also investigated owing to the different strain hardening behaviour of the two materials. The compression texture in nickel and copper was characterized by the presence of <101> component at low strain rates. At high strain rate, ~10+3 s-1, there was a decrease in the intensity of the <101> component for nickel but it strengthened for copper. This has been explained on the basis of continuous dynamic recrystallization in copper. The torsion texture evolution in nickel and copper was similar at low strain rate (10-3 s-1) and was characterized by the presence of important shear texture components. At high strain rate (1 s-1), texture weakened for nickel, while for copper a rotated cube component was observed which has been attributed to dynamic recrystallization. The effect of strain rate was studied more comprehensively in hexagonal titanium by adding one more variable, that is, the initial texture. Extreme strain rates were imparted using static and dynamic compression tests. It was found that different initial textures led to different mechanical response in terms of yield strength and strain hardening as well as microstructural response in terms of twin fractions. The samples deformed at high strain rate showed increased twinning that led to some scatter in the texture components compared to low strain rate deformed samples. VPSC simulations were able to successfully capture the evolution of texture as well as microstructural evolution in terms of twin activity in the deformed samples at the extreme strain rates. Torsion tests on titanium at different strain rates indicated evolution of inhomogeneous nature of fibre texture components with increase in strain rate. Thus, weakening of texture was observed irrespective of the strain path (compression or torsion) and crystal structure (FCC or HCP) unless additional restoration mechanism like recrystallization (continuous or discontinuous) intervened. In chapter 5, the evolution of rolling texture in two phase FCC + BCC (Ni-Fe-Cr alloys) and HCP + BCC (Ti-13Nb-13Zr ) alloys has been studied. This study was aimed at examining the effect of second deforming phase on the texture evolution in the primary phase. The effect of various parameters like volume fraction and morphology of the second phase on deformation texture evolution was studied experimentally as well as by VPSC simulations. A reduction in the Brass component of texture was observed in the austenite phase due to the presence of harder ferrite phase while a characteristic rolling texture evolved in the ferrite phase. It has been established that the softer austenite phase carried maximum strain at low volume fractions of ferrite while the harder ferrite phase carried the maximum strain at higher volume fractions of ferrite. In case of the two phase HCP+BCC alloy Ti-13Nb-13Zr, both the hexagonal α and the cubic β phases showed a characteristic rolling texture irrespective of two different morphologies. For both the equiaxed and colony microstructures, the softer β phase carried the maximum strain. VPSC simulations were able to model the deformation texture evolution as well as microstructural parameters like strain partitioning and twin fraction satisfactorily for both the microstructural conditions. It was found that the deformation mechanism in one phase could be affected by the presence of the second phase and that a characteristic change in deformation texture could be produced in the presence of the second phase. Thus, a comprehensive perspective has been developed pertaining to the evolution of texture in FCC and HCP phases in the presence of a second ductile phase. The overall findings of the three investigations carried out for the thesis are summarised in chapter 6.

The combination of direct laser interference patterning (DLIP) with laser-induced periodic surface structures (LIPSS) enables the fabrication of functional surfaces reported for a wide spectrum of materials. The process throughput is usually increased by applying higher average laser powers. However, this causes heat accumulation impacting the roughness and shape of produced surface patterns. Consequently, the effect of substrate temperature on the topography of fabricated features requires detailed investigations. In this study, steel surfaces were structured with line-like patterns by ps-DLIP at 532 nm. To investigate the influence of substrate temperature on the resulting topography, a heating plate was used to adjust the temperature. Heating to 250°C led to a significant reduction of the produced structure depths, from 2.33 to 1.06 µm. The reduction is associated with the appearance of a different LIPSS type, depending on the grain orientation of the substrates and laser-induced superficial oxidation. This study revealed a strong effect of substrate temperature, which is also to be expected when heat accumulation effects arise from processing surfaces at high average laser power.

Plastic deformation of metals and alloys are invariably accompanied by the development of texture. The origin of texture is attributed to the deformation micro-mechanisms associated with processing. The face-centered cubic (FCC) metals and alloys are known to exhibit two distinct types of textures when subjected to large strain rolling deformation, namely, (i) Cu-type texture, commonly seen in high/medium stacking fault energy (SFE) materials, (ii) Bs-type texture in low SFE materials. The circumstances that could result in the formation of Bs-type texture in low SFE materials still remains an open question and no definite mechanism has been uniquely agreed upon. Apart from the SFE, grain size could also influence the deformation mechanism and hence the deformation texture. It is well known that in materials with grain sizes less than 100 nm (referred to as nano-crystalline materials), the microstructures contain large fraction of grain boundaries. This subsequently introduces a variety of deformation mechanisms in the microstructure involving grain boundary-mediated processes such as grain boundary sliding and grain rotation, in addition to slip and twinning. A clear understanding of texture evolution in nano-crystalline materials, particularly at large strains, is a topic that remains largely unexplored. The present work is an attempt to address the aforementioned issues pertaining to the evolution of deformation texture, namely, (i) the effect of SFE and (ii) the effect of grain size, in FCC metals and alloys. Nickel-cobalt alloys are chosen as the model system for the present investigation. The addition of cobalt to nickel leads to a systematic reduction of SFE as a function of cobalt content. In this thesis, three alloys of Ni-Co system have been considered, namely, nickel – 20 wt.% cobalt, nickel – 40 wt.% cobalt and nickel – 60 wt.% cobalt. For a comparison, pure nickel has also been subjected to similar study. Chapter 1 of the thesis presents a detailed survey of literature pertaining to the evolution of rolling textures in FCC metals and alloys, and chapter 2 includes the details of the experimental techniques and characterization procedures, which are commonly employed for the entire work. Chapter 3 addresses the effect of stacking fault energy on the evolution of rolling texture. The materials subjected to study in this chapter are microcrystalline Ni-Co alloys. The texture evolution in Ni-20Co is very similar to pure Ni, and a characteristic Cu-type rolling texture is observed. The evolution of texture in these materials is primarily attributed to the intense dislocation activity throughout the deformation stages. In Ni-40Co, a medium SFE material, the rolling texture was predominantly Cu-type up to a strain of ε = 3 (95% thickness reduction). However, beyond this strain level, namely at ε = 4 (98%), the texture gets transformed to Bs-type with orientations maxima predominantly close to Goss ({110} <001>) position. Simultaneously, the Cu component which was dominant until 95% reduction has completely disappeared. The analysis of microstructures indicate that deformation is mostly accommodated by dislocation slip up to 95%, however, at ε > 3, Cu-type shear bands get initiated, preferably in the Cu-oriented ({112} <111>) grains. The sub-grains within the shear bands show preferred orientation towards Goss, which indicates that the Cu component should have undergone transformation and resulted in high fraction of Goss component. In Ni-60Co alloy, Bs-type texture forms in the early stages of deformation (ε ~ 0.5) itself and further deformation results in strengthening of the texture with an important difference that the maximum in orientation distribution has been observed at a location close to Goss component, rather than at exact Bs-location. The development of Bs-type texture is accompanied by the complete absence of Cu and S components. Extensive EBSD analyses show that the deformation twinning gets initiated beyond 10% reduction and was found extensively in most of the grains up to 50% reduction. At higher strains, tendency for twinning ceases and extensive shear banding is observed. A non-random distribution of orientations close to Goss orientation was found within the shear bands. The near-Goss component in the Ni-60Co alloy can be explained on the basis of deformation twinning and shear banding. Thus, a reasonable understanding of the deformation texture transition in the extreme SFE range has been developed. In chapter 4, the effect of fine grain size on the evolution of rolling texture has been addressed. Nanocrystalline (nc) nickel-cobalt alloys with a mean grain size of ~20 nm have been prepared by pulse electro-deposition method. For a comparison, nc Nickel (without cobalt) with similar grain size has also been deposited. For all the materials, a weakening of the initial fiber texture is observed in the early stage of room temperature rolling (ε ~ 0.22). A combination of equiaxed grain microstructure and texture weakening suggests grain boundary sliding as an operative mechanism in the early stage of rolling. At large strain (ε = 1.2), Ni-20Co develops a Cu-type texture with high fractions of S and Cu components, similar to pure Ni. The texture evolution in Ni-40Co and Ni-60Co alloys is more towards Bs-type. However, the texture maximum occurs at a location 10° away from the Goss. The evolution of Cu and S components in nc Ni-60Co alloy takes place simultaneously along with the α-fiber components during rolling. Microstructural investigation by TEM indicates deformation twinning to be more active in all the materials up to 40% reduction. However, no correlation could be drawn between the texture evolution and the density of twins. The deformation of nc Ni-20Co alloy, is also accompanied by significant grain growth at all the stages of rolling. The increase in grain size, subsequently, renders the texture to be of Cu-type. However, Ni-40Co and Ni-60Co alloys show high grain stability. The absence of strain heterogeneities such as shear bands, and the lack of significant fraction of deformation twins indicate that the observed Bs-type texture could be due to planar slip. The increase in deformation beyond 70% reduction caused a modest reduction in the intensity of deformation texture. The microstructural observation indicates the occurrence of restoration mechanisms such as recovery/ recrystallization at large strains. The overall findings of the investigation have been summarized in chapter 5. The deformation mechanism maps relating stacking fault energy with amount of strain and with grain size are proposed for micro- and nano- crystalline materials respectively.

The subject of this work subscribes to the international preoccupation regarding the elucidation of magnetic properties of solids. The crystallographic, electronic and magnetic structures of Al-Mn-Ni alloys and compounds have been investigated by X-ray diffraction, magnetization and magnetic susceptibility measurements, X-ray photoelectron spectroscopy (XPS), and band structure calculations. The thesis is organized in 6 Chapters, followed by the summary. Chapter 1 contains a brief theoretical introduction into the magnetism of metallic systems, as well the principles of XPS. The sample preparation details and all the techniques employed in the characterization of the systems are described in Chapter 2. The next 4 Chapters contain the experimental results for Mn1-xAlxNi3, Mn1-xAlxNi, Ni1-xMnxAl, Ni0.7-xAlxMn0.3 systems.