Residual stress measurement in engineering materials and structures using neutron diffraction.

This thesis presents the determination and analysis of residual stresses, both at the macrolevel and microlevel, in different engineering materials using the neutron diffraction technique. The macrostress studied is that produced by welding in stainless steel pipes used in power plants. The objective was to see the effect of a pan-thickness repair weld on the pre-existing residual stress field generated from the original weld. The strain values were measured in the three principal directions through the pipe thickness both in the original and repair weld areas and the full stress tensors were calculated. The results show the presence of a large tensile hoop stress in the outer half thickness in and around the original weld with a peak value just below the last weld cap pass. The measured through-thickness stresses show an impressive agreement with finite element predictions. A sharp rise in the axial stress in the heat affected zone is produced by the repair treatment, particularly below the repair depth. The presence of a highly tensile axial membrane stress (~175 MPa) in the repaired area compared to a compressive one (~55 MPa) in the original weld region suggests that an overall bending has been caused in the pipe by the repair work. The through-thickness radial stress is always low with values close to zero in both the original and repair welds. The. microstress investigated is that created between the constituent phases of an Al-SiCp metal matrix composite. This study can be divided into two parts. The effect of plasticity on the fatigue crack-tip stresses, particularly the microlevel misfit stresses has been studied in the first part. All the macro and micro stress components were separated from the total stress measured by neutron diffraction in a plastically deformed and fatigue cracked specimen, both unloaded and elastically loaded conditions and they were compared with those in an undeformed and cracked specimen. 1% plastic deformation has been found to reduce the misfit stresses to almost zero in both phases. No effect of fatigue cracking and elastic loading on misfit stresses has been observed in this study. In the second part of the study, changes in microstresses in bent specimens caused by different heat treatments have been investigated. A plastic deformation of about 0.33% has reduced the misfit stress by. -35% in both phases, which is regenerated by heat treatment. The amount of regeneration depends mainly on the treatment temperature and also time. A sub-zero treatment in liquid nitrogen however, has not made any significant change in the stress states in this study

Glass forming ability and soft-magnetic properties of Fe-based glassy alloys developed using high phosphorous pig Iron

Glass forming ability (GFA) and soft-magnetic behaviour of melt-spun Fe69C5.5P11.5Mn0.4Si2.3Cr1.8Mo1B8.5 (alloy 2) and Fe68C9P12Mn1Si3Nb2B5, (alloy 3) alloys prepared using high phosphorous pig iron (h-PI, Fe80C14P2.2Mn0.4Si3.4) has been studied. The glass formation, thermo-physical and soft-magnetic properties of the alloys were analyzed for different quenching rates by varying wheel speed as 23, 26, 33, 39 and 43 m/s. The simultaneous incorporation of alloying elements (Cr, Mo, Nb) and metalloids (C, B, P, Si) transforms h-PI to complete glassy alloy, even at low quenching rates. The melt quenching rate influences the thermal parameters and Curie temperature of glassy ribbons in an opposite way. Amongst all, FeCPMnSiCrMoB glassy alloy show superior combination of higher glass transition temperature of 788 K, super cooled region of 34 K, glass Curie temperature of 552 K, coercivity less than 13 A/m and maximum saturation magnetization of 1.1 T. In addition, the annealing treatment at 758 K improves magnetic softness (1.7 A/m) of the alloy by relaxation of quenched-in stresses. The comparison of developed glassy alloy with similar Fe-glassy alloys and SENNTIX type alloys show best combination of thermo-physical and magnetic properties. The glassy alloy prepared using blast furnace high phosphorous pig iron can be used for uniformly gapped soft-magnetic cores

Surface Treatment of Industrial-Grade Magnetite Particles for Enhanced Thermal Stability and Mitigating Paint Contaminants

Pigments can retain their color for many centuries and can withstand the effects of light and weather. The paint industry suffers from issues like aggressive moisture, corrosion, and further environmental contamination of the pigment materials. Low-cost, long-lasting, and large-scale pigments are highly desirable to protect against the challenges of contamination that exist in the paint industry. This exploratory study reinforces the color and thermal stability of industrial-grade (IG) magnetite (Fe3O4). IG Fe3O4 pigments were further considered for surface treatment with sodium hexametaphosphate (SHMP). This metaphosphate hexamer sequestrant provides good dispersion ability and a high surface energy giving thermal and dust protection to the pigment. Various physicochemical characterizations were employed to understand the effectiveness of this treatment across various temperatures (180–300 °C). The X-ray diffraction, Raman, and X-ray photoelectron spectroscopy techniques signify that the SHMP-treated Fe3O4 acquired magnetite phase stability up to 300 °C. In addition, the delta-E color difference method was also adopted to measure the effective pigment properties, where the delta-E value significantly decreased from 8.77 to 0.84 once treated with SHMP at 300 °C. The distinct color retention at 300 °C and the improved dispersion properties of surface-treated Fe3O4 positions this pigment as a robust candidate for high-temperature paint and coating applications. This study further encompasses an effort to design low-cost, large-scale, and thermally stable pigments that can protect against UV-rays, dust, corrosion, and other color contaminants that are endured by building paints

A novel coating strategy towards improving interfacial adhesion strength of Cu-Sn alloy coated steel with vulcanized rubber

A comparative assessment in terms of uniformity, coating coverage and coating deposition mechanism has been carried out for two different types of Cu-Sn coatings on steel substrate with varying Sn composition (2-6.5 wt%) deposited via immersion technique, viz. (i) single layer Cu-Sn coating and (ii) double layer coating consisting of a thin Cu strike layer followed by a Cu-Sn layer. Coating morphology, surface coverage, coating-substrate interface, and coating composition at surface and along the depth were studied using laser confocal microscope (OLS), scanning electron microscope (SEM) coupled with energy dispersive spectroscope (EDS), glow discharge optical emission spectroscopy (GDOES), X-ray photoelectron spectroscopy (XPS) and cross-sectional transmission electron microscopy (TEM). Quantitative depth profiling using GDOES and surface compositional analysis via XPS suggested improvement in surface coverage in the case of double layer coatings. SEM-EDS and TEM analysis confirmed that the coating deposition was more uniform with sufficient coating penetration inside the deep roughness troughs resulting in compact and micro-porosity free interface for this type of coatings. Better adhesion strength with less variation in peel force and cohesive mode of fracture within the rubber was observed for the double layer coated samples during the peel test carried out on coated steel samples vulcanized with rubber. On the other hand, the single layer coated samples showed large variation in peel force with adhesive-cohesive or mixed mode of fracture at interface. (C) 2014 Elsevier B.V. All rights reserved

Role of Sn on the adhesion in Cu-Sn alloy-coated steel-rubber interface

Cu-Sn coatings with varying Sn content were deposited on steel substrate by immersion route and the effect of variation of Sn content and the substrate roughness on the interfacial adhesion strength of Cu-Sn-coated steel substrates vulcanized with styrene butadiene rubber were investigated. The surface roughness of the coatings did not vary compared to pristine steel substrate with change in Sn weight% in the coatings. The coated surfaces exhibited bare spots or deep trough as micro-discontinuities in the coatings, where formation of Fe2O3 was evident from SEM-EDS, AES, and XPS analysis. Microstructural study of the coating cross-section and coating-substrate interface by transmission electron microscopy of cross-sectioned samples revealed inadequate penetration of coating inside these troughs. Peel test carried out on the Cu-Sn-coated steel-rubber joints showed mixed mode i.e. adhesive and cohesive mode of interfacial fracture irrespective of the coating composition. The peel test further indicated higher interfacial adhesion strength for Cu-Sn-coated samples than pure Cu-coated samples, with an optimum adhesion strength for the coatings containing 3-4 wt.% Sn

Microstructural investigation of galvanized coatings with prior flash coating of copper on DP steels

Advanced high strength steels have gained immense importance for typical auto body structures owing to their light weight and high performance. These steels are mostly alloyed with Mn, Cr, Al, Si, etc that have a tendency to form oxides on the steel surface during annealing and result in uncoated spots during galvanizing. Various new coating processes and annealing atmospheres have been tried to improve the coatability of such steels. One such method is the use of a diffusion barrier on bare steel. The present investigation has been carried out with DP steel, having Mn content of 2 wt.% coated with copper following the replacement reaction of iron and copper. The annealing and subsequent galvanizing operations were performed using hot dip simulator. XRD and SEM analysis were done to examine the characteristics of deposited copper layer. GDOES analyses showed that inter diffusion of copper and iron took place during annealing. SEM investigations of annealed specimen showed copper depleted iron rich grain boundary regions. Different layers in the galvanized coating were investigated in great detail. The morphology of the inhibition layer of copper coated sample was found to be different compared to conventional galvanized steel although, no compositional variation was detected. The TEM analysis showed that the inhibition layer was lean in copper, as supported by the ThermoCalc Al-Fe-Cu ternary phase diagram showing negligible solubility of copper in Fe2Al5 crystals. The copper was found to be distributed in the overlay zinc coating. TEM elemental mapping revealed segregation of copper at different regions of overlay zinc. The bright field and dark field images confirmed the presence of nano size precipitates within zinc coating. Finally a schematic illustration of the probable mechanism for formation of inhibition layer and copper rich zinc coating in presence of a prior copper coating was formulated. (C) 2015 Elsevier B.V. All rights reserved

Microstructural evolution in Cu-Sn coatings deposited on steel substrate and its effect on interfacial adhesion

The objective of the present work is to understand the microstructural evolution in Cu-Sn coatings with varying Sn content (3-6.5 wt%) deposited on steel substrate via immersion coating method and its effect on interfacial adhesion with styrene butadiene (SBR) based bead rubber. The phase formation prediction in different Cu-Sn alloy systems from Pourbaix diagrams constructed using FactSage revealed the formation of higher amount of SnO2 with an increase in Sn content in the coatings. Quantitative depth profiling by glow discharge optical emission spectroscopy, microstructural characterization by transmission electron microscopy and phase analysis by grazing incidence X-ray diffraction confirmed the presence of Cu3Sn precipitates with increasing volume fraction as Sn content in coatings increases. Adhesion strength measured by performing pull-out test on the SBR rubber vulcanized Cu-Sn coated steel wire samples exhibited maximum value for Cu-5 wt.% Sn coating. The formation of Cu3Sn and SnO2 played crucial role in controlling the Cu activity at the coating-rubber interface to form optimally thick Cu-sulfide layer in Cu-5 wt.% Sn coating and thus provided the maximum adhesion strength. (C) 2014 Elsevier B.V. All rights reserved

Effect of cooling rate on the evolution of microstructure and mechanical properties of nonisothermally partitioned steels

In the present investigation, multiphase microstructures containing a combination of ferrite, martensite, retained austenite and carbides have been produced by altering the cooling rate in low alloy steels. The mechanical properties have been evaluated and correlated with ensuing microstructural features. The as-cast alloys were austenitized, hot rolled to about 93% reduction in thickness, followed by cooling to 200 °C on the run-out table. The cooling rates, namely 50 and 70 °C/s, were employed for this study. The steel plates were then cooled slowly to room temperature in a furnace to simulate the nonisothermal partitioning, similar to the hot-rolled coil cooling. The results show that the alloy with lower carbon and Mn content (Alloy-1) reveal ferrite formation (35.4 ± 4.1 vol%) at the cooling rate of 50 °C/s. However, at a higher cooling rate of 70 °C/s, ferrite formation was circumvented and the presence of martensite, retained austenite (6.3 ± 0.13 vol%) and carbides were observed. Although no significant difference was observed in the hardness and strength values for these two cooling rates, the presence of retained austenite at a higher cooling rate (i.e. 70 °C/s) led to better ductility and impact toughness. In the other alloy, with higher carbon and Mn addition (Alloy-2), the ferrite formation was considerably reduced even for the cooling rate of 50 °C/s. As a result, it showed higher hardness and strength (~1.5–2.0 times), with a concurrent decrease in the ductility and impact toughness, in comparison to Alloy-1