2) For a 0.46 wt%C Ni-Cr steel plate, show any calculations to support your responses to the following queries:
- After pouring the melt into a refractory container and allowed to furnace cool to 728°C,
calculate the fractional amounts of the equilibrated phases formed within a plate.
- For a steel with the attached time-temperature-transformation (TTT) diagram, give the processing of three steel items – one plate with a microstructure of 25% upper bainite, another plate of 100% martensite minimized for cracking, and the third plate with 75%
lower bainite.
- For 2B and 2C, sketch carefully each microstructure expected for the four plates with
all the phases identified with their corresponding temperatures.
3) For high technological industries, you evaluate metals and ceramics beyond the Fe-C alloys to more costly applications.
A. For one process, elect three alloying components for Ti alloys to give alpha-gamma
phase from an eutectoid reaction and another process, give three alloying components added to Ti to give alpha-gamma phases near a peritectoid reaction. Be sure to describe each process in not more than three sentences.
B. What alloying elements should you seek for stainless steel to have a bar or plate with martensitic phase, as well as explain why?
C. For a material of the hypersonic plane, liquid Hf-Nb-Ta alloy infuses into a B4C packed bed and reacts to form a HfB2-HfC-Nb3B4-Nb4C3-TaC-Ta3B2 composite or the same boride-carbide precipitates embedded in a Hf-Nb-Ta alloy matrix. Determine the mass of Hf, Nb, and Ta needed to give you 1 kg of Nb3B4 in metal matrix having 50at%Hf- 45at%Nb-5at%T a.
D. What two refractories or ceramics (no metals) must you consider to hold a Hf-Nb melt at 2500°C in preparation for a proper Hf/Nb ratio and a refractory to eventually add Ta to the Hf-Nb alloy in a subsequent melting of the Hf-Nb-Ta alloy at 3500°C?
E. A hafnium-niobium melt contained in a graphite or carbon crucible (1 cm thick and 5 cm inner diameter) reacts to form an internal layer composed of HfC and NbC between the Hf-Nb liquid and the internal, graphite crucible. The figure below gives the diffusion coefficients of carbon in cm2/s for HfC, TaC, NbC and ZrC.
- Determine the carbon diffusion in HfC at 3600°C.
- Estimate the carbide having the larger thickness in twelve hours between the
Hf-Nb liquid and the internal crucible wall?
F. From the Ta-C phase diagram, below, give the three-phase reactions for a eutectic,
peritectic, peritectoid, congruent, and euctectoid reactions along with their respective temperatures at which they occur.
4) . A Ta2O5 semiconductor at temperatures greater than 1000°C exists with doubly- charged, oxygen vacancies. Your engineering colleague argues strongly that these oxygen ionic defects convert the tantalate lattice into a p-type semiconductor – is he correct and give reasoning?
B. Is the semiconductor n-type or p-type, if Al2O3 is added, instead of Ta2O5, to the NbO lattice and give your reasoning?
