Defects and Properties of Cast Metals: Defects I - Molten Metal and Inclusions
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Solidification Committee
Program Organizers: Lang Yuan, University of South Carolina; Brian Thomas, Colorado School of Mines; Peter Lee, University College London; Mark Jolly, Cranfield University; Alex Plotkowski, Oak Ridge National Laboratory; Charles Monroe, University of Alabama Tuscaloosa
Monday 8:00 AM
February 24, 2020
Room: 17B
Location: San Diego Convention Ctr
Session Chair: Mark Jolly, Cranfield University; Jan Frenzel, Ruhr University Bochum
8:00 AM Introductory Comments
8:05 AM Invited
Crystal Mosaicity in Single Crystal Ni-based Superalloys: Jan Frenzel1; Philipp Hallensleben1; Felicitas Scholz1; Pascal Thome1; Gunther Eggeler1; 1Ruhr University Bochum
We investigate the evolution of crystal mosaicity, i.e. the spread of crystal plane orientations, during seeded Bridgman processing of technical Ni-based single crystal superalloys (SXs). We combine solidification experiments performed at different solidification rates with advanced optical microscopy and quantitative image analysis. The results obtained in the present work show that crystal mosaicity is caused be dendrite deformation during solidification. Individual SXs have unique mosaicity finger prints. Most crystals differ in this respect, even when they were produced using identical processing conditions. Small differences in the orientation spread of the seed crystals and small stochastic orientation deviations continuously accumulate during solidification. Direct evidence for dendrite bending in a conventional solidification process is provided. It was observed that continuous or sudden bending events affect the growth directions of dendrites. We provide evidence which shows that some dendrites continuously bend by 1.7° over a solidification distance of 25 mm.
8:35 AM
In-situ Tomographic Investigation of Co-base Alloy Solidification Features: Tim Wigger1; Mohammed Azeem2; Shyamprasad Karagadde3; Zhipeng Guo4; Robert Atwood5; Nghia Vo5; Peter Lee1; 1University College London; 2University of Leicester; 3Indian Institute of Technology Bombay; 4Tsinghua University; 5Diamond Light Source Ltd
Co-base alloys are emerging as alternatives for critical components in high temperature applications, such as gas turbine blades in aeroengines. Understanding the grain nucleation, growth kinetics and morphology during solidification is crucial for accelerating the development of these novel alloys. In this investigation, we used in situ high-speed synchrotron tomography to investigate the nucleation and growth behaviour of alpha-Co dendrites during solidification. Dendrite nucleation and growth were captured as a function of the cooling rate. The alpha-Co grain nucleation, distribution of grains, growth velocities, tip radii, dendritic arm spacing, crystallographic orientation and porosity during late stages of solidification were captured and quantified. The results used to inform and validate models of the nucleation and solidification kinetics. The results are posited to provide valuable insights and data for the development of Co-base alloys and for improving solidification models for high temperature alloys.
8:55 AM
An Experimental Characterization of Thermophysical Properties of a Porous Ceramic Shell Used in the Investment Casting Process: Christopher Jones1; Mark Jolly1; Anders Jarfors2; Mark Irwin3; 1Cranfield University; 2Jonkoping University; 3TPC Components AB
Predicting defects that develop during casting processes using computer simulations is becoming increasingly commonplace in the foundry industry. This provides a cost-effective alternative to pouring a potentially large number of trial castings. However, such simulations are only viable as predictive tools if they are supplied with appropriately accurate material property data. This study presents the results of an investigation which characterizes the thermophysical properties of an investment casting mould with a zirconium dioxide/cobalt aluminate prime coat in combination with fused silica/fibre reinforced backup coats. The specific heat capacity (Cp) and thermal diffusivity (α) were determined using differential scanning calorimetry (DSC) and laser flash analysis (LFA) experimental techniques respectively from which the thermal conductivity (λ) is derived. A commercially available computational fluid dynamics (CFD) simulation package was used in combination with these thermophysical properties to predict the temperature distribution within the mould before making direct comparisons to an experimental casting as validation.
9:15 AM
Influence of Casting Conditions on Crack Sensitivity of Micro-alloyed Steel Slabs During Continuous Casting: Hossam Shafy1; Heinz Palkowski1; 1Clausthal University of Technology
Different steel grades are subjected to cracking, taking place in the casting shop or even on the route to hot rolling. One of the causes is their low ductility during slab straightening between 700 °C – 1100 °C which might lead to surface cracking. The presence of titanium and niobium precipitates is believed to influence the hot ductility during unbending. To evaluate the influence of straightening, temperature, secondary cooling and deformation rate on hot ductility, hot tensile testing was performed under varied combinations of the parameters for two steel grades (A: 0.08% C, 0.12% Ti and 0.05% Nb; B: 0.08% C and 0.001% Ti) using TM simulator DIL805T. The effect of thermal cycle and deformation on the precipitates and fracture surface were investigated by means of LOM, SEM and EDX analysis. It could be shown that –under constant secondary cooling conditions- reducing the casting speed is detrimental to hot ductility.
9:35 AM Break
9:55 AM
Spatially Resolved Compositional and Isotopic Analysis of As-cast Metallic Nuclear Fuels: Elizabeth Kautz1; Vineet Joshi1; Curt Lavender1; Arun Devaraj1; 1Pacific Northwest National Laboratory - PNNL
Impurities in as-cast metallic nuclear fuels can significantly impact microstructure formed during fuel processing, and ultimately in-reactor performance. Thus, understanding the influence of such impurities on the microstructure of nuclear fuels, including the composition and isotopic abundances of impurity phases are important in development of material processing steps that improve fuel foil quality and in turn their irradiation performance. Here, impurities in an as-cast, low-enriched metallic uranium fuel alloyed with 10 wt% molybdenum (U10Mo) are studied. In order to address when, where, and how impurity elements lead to second phase precipitation in castings, detailed compositional and isotopic analysis was performed using atom probe tomography
10:15 AM
Defects Comparison between Single and Double-sided Electron Beam Welded Dissimilar DP600 Steel to 5754 Al Alloy Joints: X-ray Tomography Study: Soumitra Dinda1; Prakash Srirangam2; Gour Gopal Roy1; 1Indian Institute of Technology Kharagpur; 2Warwick Manufacturing Group
DP600 steel to Al-5754 alloy dissimilar welding was performed using electron beam welding process at single and double sided welding with different welding speed condition. Two major weld defects i.e. porosity and intermetallic compounds (IMCs) were characterized qualitatively and quantitatively in 3-dimensional by X-ray computed tomography (XCT) analysis. It was found that both defects size and volume percentage increases with increasing welding speed. But number density of IMCs were comparatively less at higher speed but average volume quite high. Comparison with single-sided welding, double-sided welding provides quality weld products by decreasing both defects qualitatively and quantitatively. Pores more homogeneously distributed at double-sided welded products rather than single sided. Chances of gaseous pores formation highest at highest welding speed condition and identified by Raman spectroscopy method. From our above study, its clear that lower speed provides quality products. Also, double sided welding gives better products even in higher welding speed.