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The relationship between precipitate evolution, martensitic transformation temperatures, hardness, and functional load-bias behavior has been analyzed for a Ni50.8Ti34.2Zr15 (at.%) alloy. In the solutionized condition, the alloy was fully austenitic and no transformation (at least to −90 °C) was observed. Upon aging at 550 °C, the onset of a martensitic transformation (Ms), as determined by differential scanning calorimetry, was observed at approximately −10 °C and 75 °C after 24 and 300 h, respectively. Electron diffraction identified the precipitation of the orthorhombic H-phase within the B2 matrix. When the inter-precipitate spacing was ~12 nm, a greater undercooling was necessary to initiate the martensitic transformation due to overlapping strain fields of the precipitates. As the precipitates coarsened with aging time, a corresponding increase in the inter-precipitate spacing occurred and the chemical partitioning effects between the matrix and precipitate, as determined by atom probe tomography, began to dominate the transformation behavior resulting in an increase in transformation temperatures. For selected aging conditions, the load-biased shape memory behavior was determined under compressive and tensile loading using uniaxial constant-force thermal cycling experiments. A tension-compression asymmetry was noted with larger transformation strains in tension than compression at constant stresses up to 400 MPa. A recoverable transformation strain of 3% was observed in the sample aged for 4 h at 550 °C under a tensile stress of 400 MPa, which is the largest recoverable strain currently reported for a precipitation-strengthened NiTiZr alloy.

Two experimental bcc -Cu- and B2–NiAl-precipitation-strengthened ferritic steels with 6.3 at. % and 12.4 at. % Cu + Mn + Ni + Al, 950 MPa and 1600 MPa yield strength respectively, were studied. Atom probe tomography showed that the volume fraction and number density of NiAl-type precipitates in the heavier alloyed steel (designated as CF-9 ) is ∼60–70 times greater than those in the lighter alloyed steel (designated as CF -2). This is attributed to the smaller lattice misfit between these NiAl-type precipitates and the ferritic matrix in CF- 9 due to more incorporation of Mn atoms on the Al sub-lattice in the B2 NiAl unit cell. Loading rate sensitivity of hardness was measured for CF -2, CF -9 and SAE -1090, which does not have bcc -Cu precipitates. Results show that even though CF -2 and CF -9 have double and triple the strength of SAE -1090 respectively, their hardness shows weaker dependence on loading rate. This is attributed to the presence of bcc -Cu precipitates in CF -2 and CF -9 providing athermal activation of nearby screw dislocation motion. Auger electron spectroscopy studies of CF -9 samples reveal Cu segregation on grain boundaries. The observed Cu segregation is believed to be partly responsible for the lower elongation-to-failure of CF -9 compared with CF -2.

The precipitation of the P-phase in Ni–Ti–Pd and Ni–Ti–Pt shape memory alloys has been shown to dramatically increase the martensitic transformation temperature and strength in Ni-rich ternary alloys, yet little is known about the phase's compositional stability. Therefore, the compositional limits of the P-phase have been systematically studied by varying the Pd and Ni content while maintaining the general P-phase Ti 11 (Ni + Pd) 13 stoichiometry. Each alloy was solutionized at 1050 °C followed by water quenching, and aging at 400 °C for 100 h. Four distinct phases were identified by electron and x-ray diffraction: Ti 2 Pd 3 , B2 NiTi, P- and P1-phases. The latter precipitate phases became more stable with increasing Ni at the expense of the Pd content. Atom probe tomography revealed the P-phase composition to be 45.8Ti–29.2Ni–25Pd (at.%) or Ti 11 (Ni 7 Pd 6 ) as compared to the P1-phase 44.7Ti– 45.8Ni–9.4Pd (at.%) or Ti 5 Ni 5 Pd.

A series of bulk nanostructured Fe–Ni–Zr oxide-dispersion-strengthened (ODS) alloys were synthesized using high energy mechanical alloying and consolidated using high temperature equal channel angular extrusion. The resultant microstructures are composed of nano/ultrafine or micrometer-sized grains with larger intermetallic precipitates and small Zr oxide clusters (

Creep performance of a potential heat exchanger alloy, Haynes 230 was investigated. To simulate mechanical performance of a heat exchanger, sheet material of Haynes 230 transient liquid phase (TLP) bonded together. Sheets were plated on both sides with a Ni–P compound, subsequently stacked and TLP bonded together. Duplicate creep tests show low scatter in creep results, meaning a good repeatable joint was formed by TLP bonding. Overall creep performance showed less ductility and shorter times to failure than specimens originating from plate material. Evolution of a phosphorous compound at the bond line was observed and thought to potentially reduce ductility of the TLP bonded alloy.

As the length scale of materials decreases to the nanometer regime, grain boundaries occupy a relatively larger volume fraction. Consequently, they play an important role in stabilizing nanocrystalline systems. This review looks at the role of solute segregation to grain boundaries in stabilizing such systems. In recent years, grain size stabilization from solute segregation has led to new types of thermodynamic stability maps as a materials design tool. We propose to extend and adapt these concepts of grain boundary solute segregation as a stabilizing effect to thin film stress states. A recent study on Fe–Pt alloy films, where one species enriched the boundaries, was shown to manipulate the stress from tensile-to-compressive as a function of composition. This suggests that intrinsic segregation can be used as a tunable variable to manipulate stress states, analogous to changing film processing parameters, such as deposition rate and pressure. The application of such solute segregation is at the precipice of new opportunities in materials design of thin films.

High-strength low-carbon ferritic steels attaining a maximum yield strength of 1600 MPa by combined Cu and NiAl precipitation-strengthening were developed. The yield strength of the alloys increases monotonically with the total concentration of the principal alloying elements i.e. Mn, Cu, Ni and Al. At 12.40 at.%, a 1600 MPa yield strength is achieved after solution treatment at 950 °C followed by aging at 550 °C for 2 h. For all three alloys investigated, the hardness reached a maximum after 1–2 h aging at 500–550 °C. At peak hardness, the combined precipitation of the body-centered cubic (bcc) Cu-alloy and B2-ordered NiAl-type intermetallic precipitates is observed by atom probe tomography (APT). The morphology, composition and structure of the Cu-alloy and NiAl-type precipitates were characterized using APT and transmission electron microscopy, as a function of aging time at 550 °C. In peak hardness conditions, the equiaxed bcc Cu-alloyed precipitates contain substantial amounts of Fe and are enriched in Ni, Al and Mn. Ni and Mn segregate at the Cu-alloy precipitate/ferrite matrix interface. In addition to the segregation, B2 NiAl-type precipitates nucleate at the Cu-alloy precipitates. After aging for 2 h, most Cu-alloy precipitates have a NiAl-type precipitate attached to their side. On subsequent further aging, the Cu-alloyed precipitates enrich progressively with Cu and elongate, indicating a transformation to the 9R or face centered cubic structure. The Cu-alloyed precipitates coarsen slower than the NiAl-type precipitates due to interfacial energy differences between the two types of precipitates, slower diffusion kinetics of Cu through the NiAl precipitates, different matrix equilibrium solubility and solute transfer from Cu-alloyed precipitates to NiAl-type precipitates. The relatively slow growth and coarsening of Cu-alloyed precipitates are consistent with the observation of an only modest decrease of hardness with extended aging.

The effects of varying Co thickness on the mass resolving power for Cu in a multilayer stack are characterized by laser-assisted atom probe. As the Co layer thickness increased, Cu exhibited poorer mass resolving power. By reducing the pulse repetition rate from 250 kHz to 10 kHz, the mass resolving power improved to match that of Cu with no Co underlayer. These results support that thermal mechanisms for field evaporation dominate in this Co–Cu multilayer, which is a common architecture in giant magneto-resistance thin film devices.