Q2. What are the future works in "University of birmingham influence of heat treatment on microstructure and tensile behavior of a hot isostatically pressed nickel-based superalloy" ?
Tensile deformation at 700℃ was mainly due to the formation of extended stacking faults across both γ and γ′.
Q3. What is the need for jet engines to operate at higher temperatures?
The need for jet engines to operate at higher temperatures to increase efficiency requires the development of nickel-based superalloys containing increased amount of the main strengthening elements such as Ti, Al, Mo, W, Ta and Hf.
Q4. Why did the flat fracture surface fail at 700°C?
The flat fracture area could be due to plane strain conditions while the slant fracture part is because of plane stress conditions [24].
Q5. What was the process of HIPeding on stainless steel cans?
HIPing was carried out on stainless steel cans with a length of 180mm and an inner diameter of 45mm which after filling with powder, to a tap-density of between 60 and 65%, was outgassed and sealed by closing the evacuation tube by welding.
Q6. What are the main properties of HIPed nickel-based superalloy powder?
directly HIPed nickel-based superalloy powder usually suffers from PPBs decorated with carbides, oxides or oxycarbides which are harmful to mechanical properties, especially the hot ductility, low cycle fatigue and stress rupture properties [10-14].
Q7. What is the reason for the change in the microstructure of as-HIPed samples?
The dominant coarse and irregular-shaped primary and secondary γ′ precipitates in as-HIPed samples were replaced with a large volume fraction of finer cuboidal secondary γ′ and spherical tertiary γ′.
Q8. What is the effect of ageing on secondary ′?
Solution treatment at (S-40)°C (STA) plus ageing considerably decreased the volume fraction of secondary γ′ and changed the irregular-shaped γ′ in the as-HIPed samples into cuboidal or near-triangular morphology.
Q9. What is the main reason for the reduction in hot workability of nickel-based superallo?
increased alloying usually leads to extensive segregation in the cast ingots which results in significant reduction in their hot workability.
Q10. What is the reason for the thermally induced pores?
Given that the thermally induced pores are mainly located at grain boundaries, they are believed to be formed due to boron-induced incipient melting at grain boundaries [18-19].
Q11. What is the effect of the treatment of HIPed RR1000?
Solution treatment at 40°C below γ´ solvus together with ageing at 760°C completelytransformed the coarse and irregular-shaped γ′ in as-HIPed RR1000 samples into finer cuboidal secondary γ′ and medium-sized tertiary γ′.
Q12. What was the cooling rate of the HIPed samples?
Some HIPed samples were solution-treated for 2h at (S-40)°C and S, respectively, after which the samples were air cooled (the cooling rate was measured to be around 105ºC/min).
Q13. What is the size range of the powder used in this study?
The powder used in this study is an argon-atomised nickel-based superalloy powder RR1000 which has a size range below 53µm in diameter.
Q14. What is the reason for the fracture at 700°C?
As compared with the room temperature fracture, fracture at 700℃ is more faceted and crystallographic which suggests that the deformation at elevated temperature is more planar, consistent with the above observation on deformation.
Q15. What was the process used to examine the structure of the samples?
The samples were polished and chemically etched in activated colloidal silica solution and cleaned in acetone and then examined using a JEOL 7000 FEG-SEM microscope to study the structural integrity.
Q16. Why do some of the coarse precipitates in the as-HIPed samples remain after solution treatment?
Some of the coarse precipitates present in the as-HIPed samples in fact remain after solution treatment because this temperature is below the γ′ solvus.
Q17. What was the common cause of the stacking faults?
Many of the stacking faults even extended across the γ channel into the adjacent tertiary γ′precipitates and formed complex arrays of faults.
Q18. What is the way to reduce the cost of producing components from powder?
Net-shape HIPing [1-5] offers a possible solution to this high cost of producing components from powder since this would lead to the reduction in forging and machining operations and thus to considerable cost reduction.
Q19. What is the reason for the deformation of the samples?
The TEM study of the deformed samples generally showed behavior very similar to that reported in many papers of deformed Ni superalloys, with shearing through and looping of dislocations around γ′ precipitates.
Q20. What is the main reason for the improvement in tensile properties of HIPed ?
The current study demonstrates that with proper processing conditions, desirable microstructure and mechanical properties for net-shape HIPed Ni-based superalloys could be achieved.•
Q21. What is the reason why the HIPed was designed to produce a minimum stacking fault?
This is possible since the superalloy investigated in the present study was designed to produce a minimum value of stacking fault energy through maximum addition of Co to promote planar slip and to inhibit cross slip, which are beneficial for both crack growth rates and creep behaviour [22].
Q22. What is the effect of ageing on primary and secondary ′?
Ageing treatment generally shows no influence on primary and secondary γ′ in both as-HIPed and solution treated samples but seems to increase the population of fine tertiary γ′ (Fig.1 (d)).