Stan David - Academia.edu (original) (raw)

Papers by Stan David

The phase selection phenomenon as a function of interface growth velocity was investigated in an ... more The phase selection phenomenon as a function of interface growth velocity was investigated in an Fe-C-Al-Mn self-shielded flux cored arc weld metal deposit. In this steel, under normal weld cooling conditions, the primary solidification occurs by d-ferrite formation. With an increase in liquid-solid interface velocity a transition to nonequilibrium austenite solidification was observed. The above phase selection phenomenon was tracked in-situ using a timeresolved X-ray diffraction technique employing Synchrotron radiation. Using the theoretical treatment of dendritic solidification and phase selection maps advanced by Kurz and his coworkers, the microstructure evolution at high weld solidification rates was evaluated.

Portions of this document may be illegible in electronic image products. Images are produced from... more Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

Microscopy and Microanalysis

Weldability of single-crystal and directionally solidified Ni-base alloys is important for repair... more Weldability of single-crystal and directionally solidified Ni-base alloys is important for repairwelding of failed components. During welding, phase decomposition and subsequent microstructure development may occur under non-equilibrium conditions. The final microstructure and phase composition of γ and γ' phases in these welds control the weld properties. Previous work used atom-probe field-ion microscopy (APFIM) for characterizing commercial single-crystal alloys. This work summarizes the microstructural development in PWA-1480 [Ni - 11.5 at. % Cr - 11.0% A1 - 5.1% Co - 1.3% W - 1.9% Ti - 4.0% Ta] electron beam (EB) welds and CMSX-4 [Ni - 7.5 at. % Cr - 12.7% A1 - 9.9% Co - 0.38% Mo -2.1% W - 1.3% Ti - 2.2% Ta - 0.95% Re - 0.034% Hf| pulsed laser (PL) welds.In both PL and EB welds, a dendritic mode of weld solidification was observed.

Scripta Metallurgica et Materialia

MRS Proceedings

ABSTRACTA finite-difference implicit numerical model was used to study the diffusion-controlled α... more ABSTRACTA finite-difference implicit numerical model was used to study the diffusion-controlled α-γ solid-state phase transformation in the Fe-Cr-Ni system. The influence of a non-uniform initial composition distribution was examined in order to assess the impact that non-uniform solute profiles resulting from solidification may have on subsequent transformation behavior in weldments and castings. A significant impact on the transformation kinetics and transformation path was found in some cases. The factors that affect the degree of influence are discussed.

Science and Technology of Welding and Joining

ABSTRACT Nanostructured ferritic alloys, which have complex microstructures consisting of ultrafi... more ABSTRACT Nanostructured ferritic alloys, which have complex microstructures consisting of ultrafine ferritic grains with a dispersion of stable oxide particles and nanoclusters, are promising materials for fuel cladding and structural applications in the next generation nuclear reactor. This study evaluates microstructure of friction stir welded nanostructured ferritic alloys using electron microscopy and atom probe tomography techniques. Atom probe tomography results revealed that nanoclusters are coarsened and inhomogeneously distributed in the stir zone and thermomechanically affected zone. Three hypotheses on coarsening of nanoclusters are presented. The hardness difference in different regions of friction stir weld has been explained.

Science and Technology of Welding and Joining

Abstract: The welding behaviour of alloy PWA 1480, a single crystal nickel base super alloy, has ... more Abstract: The welding behaviour of alloy PWA 1480, a single crystal nickel base super alloy, has been investigated. The ability to successfully weld single crystal nickel base superalloys is desirable for fabrication procedures as well as for potential repair applications in both ...

Science and Technology of Welding and Joining

ABSTRACT Iron aluminides are susceptible to hydrogen cold cracking during gas tungsten arc weldin... more ABSTRACT Iron aluminides are susceptible to hydrogen cold cracking during gas tungsten arc welding. Fine grained base materials have been shown to be more resistant to environmental embrittlement when tested in the presence of water vapour than coarse grained base materials. To study the effect of fusion zone grain size on cold cracking susceptibility, welds were produced using magnetic arc oscillation to refine the fusion zone grain structures. Tensile tests were conducted in varying water vapour atmospheres, on weldments with average fusion zone grain sizes ranging between 115 and 530 μm. Fracture strength data followed Hall–Petch behaviour and the effect of water vapour concentration was also incorporated into the traditional plot. The results of the tensile tests showed the finer grain size fusion zones were less susceptible to hydrogen cracking and more tolerant of high hydrogen concentration than coarse fusion zone grain structures.

Scripta Metallurgica et Materialia

recrystallization annealing temperature was raised to 1000"C, the rupture life was greatly reduce... more recrystallization annealing temperature was raised to 1000"C, the rupture life was greatly reduced (Table 3). Only the FA-385 alloy of the new group was creep-tested at 593"C/138 MPa, and it was much less creep-resistant than FA-362, but was still better than FA-32.4 and slightly better than FA-350. Vol. 27, No. 12 WELDING BEHAVIOR OF FeAI ALLOYS

MRS Bulletin, 1994

Welding is utilized in 50% of the industrial, commercial, and consumer products that make up the ... more Welding is utilized in 50% of the industrial, commercial, and consumer products that make up the U.S. gross national product. In the construction of buildings, bridges, ships, and submarines, and in the aerospace, automotive, and electronic industries, welding is an essential activity. In the last few decades, welding has evolved from an empirical art to a more scientifically based activity requiring synthesis of knowledge from various disciplines. Defects in welds, or poor performance of welds, can lead to catastrophic failures with costly consequences, including loss of property and life.Figure 1 is a schematic diagram of the welding process showing the interaction between the heat source and the base metal. During the interaction of the heat source with the material, several critical events occur: melting, vaporization, solidification, and solid-state transformations. The weldment is divided into three distinct regions: the fusion zone (FZ), which undergoes melting and solidifica...

Microscopy and Microanalysis

Scripta Metallurgica et Materialia

MRS Proceedings

Science and Technology of Welding and Joining

Scripta Metallurgica et Materialia

MRS Bulletin, 1994