Francis S. Biancaniello

The Al-Cu-Fe phase diagram: 0 to 25 At. pct Fe and 50

Isothermal sections of the Al-Cu-Fe equilibrium phase diagram at temperatures from 680 °C to 800 °C were determined in the region with 50 to 75 at. pct Al and 0 to 25 at. pct Fe using scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) techniques. This re- gion includes the face-centered icosahedral phase (Ψ-Al6Cu2Fe) which has unprecedented struc- tural perfection and no apparent phason strain. The icosahedral phase has equilibrium phase fields with four distinct phases at 700 °C and 720 °C (β-Al(Fe, Cu), λ-Al13Fe4, ω-Al7Cu2Fe, and liquid) and three phases at 680 °C(β, ω, and λ) and 800 °C (β, λ, and liquid). The B2 ordered β phase has considerably greater solubility for Cu than previously reported, extending from AlFe to ∼Al50Fe5Cu45. The equilibrium range of composition for the icosahedral phase at these temperatures was determined, and a liquidus projection is proposed.

Icosahedral Al-Mn and related phases: resemblance in structure

Etudes preliminaires des relations cristallographiques entre les phases icosaedrique, T, T″ et Al 4 Mn par microscopie electronique en transmisssion a haute resolution

Stacking faults and crystallite size in mechanically alloyed Cu-Co

Abstract Mechanically alloyed CuCo (5–90 wt.% Co) has been analyzed using X-ray diffractometry to study microstructural features. All compositions were single phase face-centered cubic. Although some of the observed peak broadening can be attributed to fine grain size and microstrain effects, anomalous hkl-dependent peak broadening and peak shifts are clearly associated with stacking faults. Furthermore, the true grain sizes were > 100 nm, 3–10 times the grain size calculated without considering stacking fault contributions.

Observations on crystal defects associated with diffusion induced grain boundary migration in CuZn

Abstract Standard TEM techniques have been applied to the study of crystal defects associated with DIGM in copper foil exposed to zinc vapor. The experimental results have been compared to the coherency strain theory (as discussed for liquid film migration (15, 16) and the Balluffi/Cahn GB Kirkendall effect theory (11). There are indications that coherency strain may play a role in the initiation of DIGM but the observation of a high density of GB steps suggests GBD climb is also a viable mechanism. However, neither model can explain all the experimental results. None of the current theories can be proved or disproved on the basis of the results presented here. The observations do, however, suggest the possibility that more than a single mechanism or driving force may be responsible for all the morphological changes associated with DIGM. We hope that this paper will serve to stimulate further TEM analysis of the DIGM process, particularly in the area of grain boundary structure and matrix dislocation densities.

Process control during high pressure atomization

Abstract High pressure inert gas atomization (HPIGA) has been studied using various metal alloy systems. The high yield of ultrafine (particles less than 45 μm in size) powder produced using HPIGA makes it an ideal system for producing rapidly solidified metal powder. High speed photography and laser scattering techniques have been applied to study droplet formation and measure powder size with the intent of future feedback and control of particle size during atomization. Liquid metal droplet formation will be discussed as well as on-line particle size measurement and control.

Fiber and interface fracture in singlecrystal aluminum/SiC fiber composites

Model metal-matrix composite tensile specimens, each containing a single SiC fiber in a single crystal of pure Al, were grown using a modified Bridgman method at two growth rates and with various fiber surface treatments in order to study their effect on fiber and interface strength. Using the load drops in tensile tests, we measured both fiber and interface strengthin situ. Acoustic emission (AE) was monitored to assist in determining the failure mechanisms. Both the fiber surface treatment and growth rate were found to significantly affect the fiber and interface strength. Fibers with carbon-rich outer surfaces had higher fiber strengths but lower interfacial strengths than untreated fibers. These results are discussed in terms of failure mechanisms and interfacial reactions occurring during growth of the composites.

Transformation of the icosahedral phase in rapidly quenched Al-rich AlMn alloys

Abstract Crystallization of the quasicrystalline icosahedral phase formed in Al-rich AlMn alloys has been studied by constant heating rate DTA, XRD, and TEM. Heats and activation energies of transformation were obtained, and evidence presented which suggests that the transformation is diffusion controlled.

TEM observation of icosahedral, new crystalline and glassy phases in rapidly quenched CdCu alloys

Abstract TEM study of microstructures observed in rapidly solidified CuCd alloys in the compositional range between 37.2 to 60.5 at% Cd demonstrates for the first time: 1. 1. The formation of an icosahedral CuCd quasicrystalline phase; 2. 2. The existence of a tetragonal CdCu phase first identified by x-ray diffraction by Dey and Quader as the Cd 3 Cu 4 phase. 3. 3. The existence of a new CuCd cubic fcc phase with a giant unit cell of a ≅ 3.25 nm, close to the Cd 3 Cu 4 composition. 4. 4. Formation of Cu-37.2 at% Cd metallic glass. 5. 5. The possibility of forming giant unit cell crystalline structures from the melt and by solid-state precipitation during the limited times of rapid quenching.

Quasicrystalline coatings: Thermal evolution of structure and properties.

Quasicrystals (QCs) are known to exhibit unique properties as a result of their unique quasiperiodic structure. Real quasicrystalline (QC) materials, however, may exhibit complex phase structures, and as a consequence, their properties may differ from expectations. In the present work, QC coatings of the Al–Cu–Fe, Al–Cu–Fe–Cr, and Al–Pd–Mn systems were prepared by a plasma spray process, followed by heat treatments in the range 500–800 °C. The phase structure and evolution of the coatings were evaluated, and thermal diffusivity, hardness, and friction coefficient were measured. The presence of quasicrystalline and crystalline phases and their influence on these properties is systematically considered for the first time. Broadly, the coatings exhibit the properties expected of QC materials, low thermal diffusivity, high hardness, and low coefficients of friction, but it is also shown that these properties can be sensitive to the phase structure of the coatings. This suggests that phase structure may be manipulated by heat treatment to optimize the properties of QC coatings.

Beneficial effects of nitrogen atomization on an austenitic stainless steel

Fully dense nitrogenated austenitic stainless steels were produced by gas atomization and HIP consolidation. The base alloy, 304L, contained about 0.15 wt pct nitrogen when melted under a nitrogen atmosphere, and a modified version of 304L with 23 wt pct Cr contained 0.21 wt pct nitrogen. A series of experiments using various combinations of N2 and Ar as the melt chamber backfill gas and atomizing gas demonstrated that the nitrogen content of the powder was largely controlled by the backfill gas and that the fraction of hollow particles was determined by the atomization gas. The hollow powder particles, which are common in inert-gas atomized materials, were virtually eliminated in the nitrogen atomized powders. Additional atomizing experiments using copper and a nickel-base superalloy indicate that low gas solubility in the metal leads to gas entrapment. Hardness and compression behavior (yield strength and flow stress) are substantially improved with the addition of nitrogen. The results of this study suggest that the properties of nitrogenated stainless steels fabricated in this manner are comparable to other high nitrogen austenitic alloys.