50nm 200nm Secondary  ´ Tertiary  ´ Matrix  Atom probe studies of linear cooled samples (Rene 104) - some observations Motivation for work: Understand effects of cooling rate on microstructure Microstructural changes can induce changes in deformation mechanisms Typical 3D atom probe reconstruction 30 o F/min 250 o F/min400 o F/min

     (precipitate) Ni Co Cr Al Ti Ta W Mo Proximity histograms (proxigrams)      matrix      phase Which elements in to which phase Partitioning of an element to an element can be different of different alloys (Sudbrak et al’s work) Partitioning ratio Used on non-planar interfaces

Ta W Mo Tantalum concentration profile 400 o F/min250 o F/min30 o F/min ’’  Tantalum concentration variation extends beyond other element concentration profiles Extended even for aged sample Also seen by Sudbrack et al with Cr 400 o F/min + aged

Ta W Mo W - segregation 400 o F/min 250 o F/min 30 o F/min 400 o F/min o C/8hrs Tungsten concentration (at.%) Distance (nm) Tungsten concentration (at.%) Distance [nm] W 400 o F/min Sudbrak et al observed W enrichment Disappeared after ageing at 800 o C/1hr Dieter et al 2004 found no enrichment observed in Rene 88 DT Rhenium has been found to segregate to the g/g’ interface in Blade alloys

Compositional profile of tertiary  ’ (from 30 precipitates)   Compositional profile across a secondary  ’ and matrix interface Results indicate a wider  /  ’ interface for the tertiary  ’ than for the larger secondary  ’ ’’ ’’ Interface width

Contour plot of ISF energy versus at.% concentration of Co and Cr Total Co and Cr concentration ~50at.% in  -matrix (a lot) more than Ni Matrix contains 30 at. Cr and 25 at.% Co. Based on old experimental results from Beeston et al, Smallman al and Harris et al Significance of phase composition ISF energy is around 25mJ/m 2

Al Ti Ni Crystal ordering Site occupancy concentration of Ti in Al sublattice is high What are the effects of Ti on CSF energy ? Ni 3 Al (L1 2 ) and Ni 3 TI (DO 24 ) have different crystal structures Little work in the literature R.C Reed suggest that Ti increases APB ?

CooledCooled + agedCooled + really aged Localized coarsening (unaffected by secondaries) Global coarsening (affected by secondaries) Effect of ageing on cooled samples How does the initial “cooling tertiaries” number density affect number density and thus final volume fraction of tertiary  ’ ?

Questions and possible future work with atom probe tomography What are the implications of diffuse  /  ’ interfaces ? How can this and other parameters be used in models How significant and prevalent are these ultra ultra fine (~1nm)  ’ precipitates w.r.t. creep? How stable are these  ’ precipitates ? Are they sub or supercritical nuclei ? Can altering the cooling profile (linear. Non-linear) alter the Vf and number density of the tertiary  ’ precipitates? What are the affects of Ti of CSF energy

Apply atom probe analysis to stacking faults Is there segregation at these faults? Isothermal ageing studies to understand: growth kinetics (for phase-field group) Critical nucleation size