After a short review on temperature dependence of the intrinsic coercivity in sintered Nd–Fe–B-type magnets is given, recent experimental results concerning the coercivity-anisotropy (HC–HA) correlation in B-rich Pr–Fe–B and Nd–Fe–B sintered magnets and the influence of the surface conditions of the sintered Nd–Fe–B magnets on the coercivity are reported. The results are interpreted in terms of the μoHc vs cμoHA – NIs plot, where Is is the spontaneous magnetization of R2Fe14B (R = Pr or Nd) and N is the effective demagnetization field coefficient.

Pulsed nuclear magnetic resonance (NMR) proved to be a complementary new technique for the study of moving dislocations in Al–Mg–Zn alloys. The NMR technique, in combination with transmission electron microscopy (TEM), has been applied to study dislocation motion in Al–0.6 at. % Mg–1 at. % Zn and Al–2 at. % Mg–2.5 at. % Zn. Spin-lattice relaxation measurements clearly indicate that fluctuations in the nuclear quadrupolar interactions caused by moving dislocations in Al–Mg–Zn are different compared to those in ultra pure Al. From the motion induced part of the spin-lattice relaxation rate the mean jump distance of mobile dislocations has been determined as a function of strain. From the NMR data it is concluded that moving dislocations advance over a number of solute atoms in these alloys as described by Mott-Nabarro's model. At large strains there exists a striking difference between the mean jump distances in Al–0.6 at. % Mg–1 at. % Zn and in Al–1.2 at. % Mg–2.5 at. % Zn. The latter is about five times smaller than the former one. This is consistent with TEM observations that show dislocation cell formation only in Al–0.6 at. % Mg-1 at. % Zn and the macroscopic stress-strain dependences of these alloys.

A well-annealed polycrystalline nickel aluminide of composition Ni–23.5Al–0.5 Hf–0.2B (at. %) shows inverse creep behavior at 1033 K and 250 MPa. The minimum creep rate does not correspond to a steady-state creep condition. The increase in the creep rate with strain and time is accompanied by an increase in the volume fraction of dislocation-containing regions. The inverse transient can be eliminated by prestraining at room temperature. It is absent in the diffusional creep regime.

The limiting substitution of Co or Fe for Cu in the orthorhombic superconducting phase YBa2Cu3O7−δ yields the tetragonal, semiconducting compositions YBa2Cu2CoO7.25 and YBa2Cu2.5 Fe0.5O7.19 after annealing at 400°C and slow cooling in O2. Single-crystal x-ray structural analyses, conductivity and magnetic-susceptibility measurements, and thermogravimetric analysis (TGA) data provide evidence for Co or Fe substitution at the Cu (1) position and intercalation of peroxide ions (O2)2− The two compositions decompose for disintercalation of oxygen beyond O6.7 for Co and O6.4 for Fe when heated in N2. The Cu(2) atoms of tetragonal YBa2Cu4O6 appear to be antiferromagnetic below a Tn ∼ 240 K, which is similar to comparable Cu–O planar nets in stoichiometric La2CuO4.

The effect of the parameters of laser irradiation (beam power and travel velocity) as well as of various surface coatings and protecting atmospheres on the size, structure, and hardness of the laser-affected region was studied in the case of commercial 1045 steel and a continuous CO2 laser. The action of the laser beam depends more strongly on its traverse velocity than on its power. When the power density exceeds a certain threshold level, a drastic decrease in the size of the laser-affected region takes place. The action can be enhanced by surface treatment in orthophosphoric acid as well as by some painted surface coatings. Unlike the latter, electroplated Cr and Ni layers were found to cause substantial alloying of the laser-treated layer. The laser-affected region formed by a single pass consists of two distinct zones: a melt zone, surrounded by an austenitization zone with a duplex structure representing former pearlite and ferrite regions. The hardness of the melt zone (about HV 750) exceeds that of conventionally hardened 1045 steel; even higher values (up to HV 900) are observed in the former pearlite regions of the austeniti zation zone, that of the former ferrite regions being about HV 250. In the case of an extended surface processed by a series of equidistant passes, a relatively wide region of tempered martensite is formed (with minimum hardness values down to HV 400) due to the heating generated by each pass in the previously hardened layer. As a result, a periodic hardness distribution is observed, whose fcatures depend on the degree of overlapping. High tensile residual stresses were found by x-ray diffraction in surface layers both in the cases of overlapping and separated passes.

The nucleation and amorphization of radiation-induced (G) and radiation-enhanced (η) phases in a silicon- and titanium-modified austenitic stainless steel have been studied under nickel-ion irradiation. These silicon- and nickel-enriched phases form under high-temperature (950 K) irradiation as the result of radiation-induced segregation to radiation-produced interstitial dislocation loops. Availability of carbon promotes the formation of η phase relative to G phase. Under lower temperature (450 K) irradiation, G and η phases are amorphized without significant change in composition of metallic elements. Two carbide phases (MC, M23C6) remain crystalline for the same irradiation conditions. The amorphization of the silicides may result from (1) radiation damage increasing their free energy above that of the amorphous state or (2) direct formation of the amorphous phase in the damage cascade.

Tracer diffusion of 60Co and 63Ni in the amorphous alloy NiZr near the equiatomic composition has been measured in the temperature range between 486 and 641 K using the ion-beam sputter-sectioning technique for serial sectioning. The temperature dependence for the diffusivities of Co and Ni in a-NiZr exhibit Arrhenius behavior; these can be expressed as follows: D∗co = 3.6 × 10−7 exp [− (135 ± 14) kJ mol−1 /RT] m2/s and D∗Ni = 1.7 × 10−7 exp [− (140 ± 9) kJ mol−1 /RT] m2/s. The values of D∗Ni are in good agreement with those measured by the Rutherford backscattering technique. The measured diffusivities were independent of time, indicating that no relaxation took place during diffusion.

Individual particles of argon-atomized Fe-30Ni powder are electrodynamically levitated and remelted by a CO2 laser pulse. The thermal history of each droplet during remelting and solidification is monitored by single-color radiation pyrometry at each of three wavelengths (850, 750, and 550 nm). Experiments are done in an atmosphere of either air or nitrogen. The average supercooling of six experiments performed in nitrogen is 298 K with a standard deviation of 14 K. This value is of the same order as several others reported in the literature using bulk levitation and emulsification techniques. The average supercooling of seven experiments performed in air is 163 K with a standard deviation of 20 K. The difference suggests that oxides are forming in the air-remelting experiments and catalyzing nucleation at relatively low supercoolings. The average cooling rate of the liquid droplets prior to solidification in nitrogen is 1.5 × 105 K/s. This measured cooling rate is somewhat higher than that predicted by Newtonian heat flow modeling, and the difference is attributed to radiative losses not considered in the Newtonian model. The measured cooling rate is used to estimate the total heat transfer coefficient characterizing cooling of a small metal droplet in a quiescent gas atmosphere. A lower bound of 1.5 × 106 K/s on the droplet heating rate during recalescence and a minimum average liquid/solid interfacial velocity during recalescence of 0.1 m/s are estimated.

Pulsed excimer laser radiation has been successfully employed in the improvement (> 50%) of fracture strength of metal-coated ceramics. Thin metallic layers (∼500 Å) of nickel were deposited on silicon nitride and silicon carbide substrates and further irradiated with pulsed excimer (xenon chloride, krypton fluoride) laser pulses. The laser energy density was varied from 0.4 to 2.0 J cm −2 to optimize the formation of mixed interfacial layers. The formation of interfacial layers was studied by transmission electron microscopy and Rutherford backscattering spectrometry techniques. Detailed heat flow calculations using implicit finite difference methods were performed to simulate the effects of intense laser irradiation on metal-coated ceramic structures. Three different mechanisms were found to play an important role in the improvement in the fracture strength of these ceramics. Theoretical calculations showed that the displacement of the crack tip away from the free surface by laser surface modification can lead to a 100% improvement in the fracture strength of the ceramic.

A treatment of diffusion limited growth of a coherent spherical precipitate into supersaturated solution is presented. It is found that the growth kinetics are affected by dilatational coherency strains and by compositionally induced strains in the matrix phase. Numerical solutions to the time-dependent problem are obtained and are compared to the quasistationary solution. The parabolic growth coefficient is a function of the transformation strain, partial molar volumes of the components, elastic constants in each phase, interfacial compositions and far-field composition while, in contrast, the growth coefficient in the absence of stress is a function only of the reduced supersaturation. Elastic effects shift the interfacial concentration of the matrix in the direction of the far-field concentration, reducing the effective driving force for growth. At the same time, compositionally induced strains increase the diffusive flux, increasing the growth rate.

An experimental technique of prestressing and quenching was employed in order to elucidate the nature of pinning points responsible for the anomalous yield strength of Ni3Al. The apparent number density of pinning points at room temperature was found to be unaffected by the prestressing and quenching from elevated temperatures. This result is consistent with the crossslip-pinning (CSP) model in that cross-slipped segments act as pinning points on the leading superpartial dislocations.

Titanium aluminum intermetallic compound is a possible candidate for a high-temperature structural material, except for a problem of lack of room-temperature ductility. Recently, this problem was found to be overcome possibly by the addition of Mn, but this mechanism has not been fully understood yet. In order to understand the fundamental mechanism of the ductility improvement by Mn addition, microanalyses have been carried out. The results are as follows. Twin structures in a TiAl intermetallic compound in the as-cast state can be climinated by high-temperature annealing, while those in Mn-added TiAl are thermally more stable and exist even after annealing for 86.4 ks at 1273 K. The reason for this thermal stabilization of twin structures is considered to be due to the pinning effect of twin dislocations by Mn addition. The enhancement of twin deformation in TiAl by Mn addition is regarded to be caused by two factors. One is the stabilization of twin partial dislocations, becoming the nucleation sites for twin formation. The other is the decrease in stacking fault energy, which makes twin deformation energetically easier.

The crystalline-to-amorphous transformation in U6Fe produced by thermal fission fragment damage was studied using resistivity and differential scanning calorimetry. The results are described in terms of a model of radiation-produced defect buildup in the crystalline matrix followed by transformation of small regions to an amorphous phase when a critical local defect concentration is reached. This can occur directly in a single cascade or from cascade overlap. The total resistivity is modeled assuming an inhomogeneous media consisting of a crystalline matrix containing a dose-dependent concentration of defects and amorphous zones. The crystallization behavior is initially, starting at Tc = 388 K, a kinetically limited process of shrinkage of amorphous zones that gradually transforms to nucleation and growth in fully amorphous material at Tc = 555 K.

Isothermal devitrification of Pd85Si15 amorphous alloys has been analyzed using differential scanning calorimetry (DSC) and x-ray diffractometry. Both as-quenched and aged amorphous ribbons were investigated. Crystallization of aged samples starts from the surface and proceeds several micrometers into the bulk. The product of this process is a layer of strongly textured palladium (111) followed by a mixture of Pd2Si, Masumoto MSI phase, and untextured palladium. Next, the crystallization occurs via a different (bulk) mechanism, resulting in a mixture of Masumoto MSII phase and untextured palladium. The bulk mechanism is the only one observed in as-quenched samples. The surface and bulk crystallization mechanisms are spatially decoupled and, therefore, the corresponding DSC data can be analyzed separately. This has been done according to the Kolmogorov–Johnson–Mehl–Avrami model and also using the recently developed concept of local value of Avrami exponent n. For both the surface and bulk crystallization the phase transition process cannot be characterized by a single value of n. Observed variation of n with the crystallized fraction x is explained by a considerable variation of the nucleation rate that takes place during devitrification.

Thin-film reactions of Co with Zr have been studied in the temperature range between 473 and 523 K by electrical conductance measurements and cross-sectional transmission electron microscopy (CS-TEM). The reduction of the electrical conductance during the solid state reaction is explained by formation and growth of an amorphous phase at every Zr/Co interface. For long reaction times the growth of the layer thickness follows a shifted $\sqrt t$ law. For short reaction times the measurements show a linear time law, which is expected for an interface limited reaction.

This paper analyzes the effect of grain size on yield stress of ordered Ni3Al and Zr3Al, and mild steels that show Lüders band propagation after yielding, using the Hall-Petch relation, σy = σ0 + kyd−½, and the new relation proposed by Schulson et al., σy = σ0 + kd −(p − 1)/2 [Schulson et al., Acta Metall. 33, 1587 (1985)]. The major emphasis is placed on the analysis of Ni3Al data obtained from published and new results, with a careful consideration of the alloy stoichiometry effect. All data, except for binary stoichiometric Ni3Al prepared by powder extrusion, fit the Hall-Petch relation, whereas the data from boron-doped Ni3Al and mild steels do not follow the Schulson relation. However, no conclusion can be made simply from the curve fitting using either relation. The results are also discussed in terms of Lüders strain and alloy preparation methods. On the basis of the Hall-Petch analysis, the small slope ky is obtained only for hypostoichiometric Ni3Al with boron, which would be related to a stronger segregation of boron in nickel-rich Ni3Al. In addition, the potency for the solid solution strengthening effect of boron is found to be much higher for stoichiometric Ni3Al than for hypostoichiometric alloys.

Numerical calculations of the diffuse scattering near Bragg reflections from coherent solute precipitates in a dilute alloy have been made. Results are presented for spherical precipitates in an elastically isotropic continous medium where the calculations have been reduced to a one-dimensional numerical integral. The scattering is separated into direct scattering from the precipitates, the Huang scattering from the lattice distortions, and the higher-order distortion scattering; calculations are presented for 50 Å radius precipitates with an internal strain of – 1.5%, and the sensitivity of the scattering to changes of the size and the internal strain of the precipitates is demonstrated. The possibility of using such scattering for the determination of the concentration, size distribution, and internal strain of solute precipitates is discussed.

Bulk polycrystalline samples of sintered Al2O3, and hot-pressed Al2O3, SiC, TiB2, and B4C ceramics were ion implanted at 77 K with 190 keV N+ to a dose of 3 × 1017 N/cm2. Nitrogen implantation resulted in reduced friction coefficients for SiC, TiB2, and B4C samples and a reduction in wear for TiB2. Both Al2O3 samples showed a significant increase in friction coefficients after nitrogen implantation. Nitrogen-implantation-induced changes in these properties appear to be correlated with the thermodynamic tendency of the sample to form “nitridelike” bonds.

Field emitter array (FEA) devices were constructed using thin-film fabrication techniques based on in situ eutectic composites containing either TaC or NbC fibers in a NiCr alloy matrix. The emission characteristics of the TaC devices were measured and compared to those of W–ZrO2 FEA's. Both devices produced the linear Fowler-Nordheim plots common to all field emission devices; however, the array current density of the TaC FEA's was more than two orders of magnitude lower than that of the W–ZrO2 FEA's. This was primarily due to the lower fiber density and lower field enhancement of the carbide fiber devices. If it were possible to produce cathode geometries comparable to those of the W–ZrO2 FEA's, a theoretical analysis indicates that emission performance of the TaC devices would be superior because of the lower work function of TaC. However, post-emission observations indicated that the carbide fiber emitters failed more readily than the tungsten emitters under comparable operating conditions.

The role of interaction between slip dislocations and a Σ = 9 tilt boundary in localized microplastic deformation, cleavage, or intergranular fracture in the Li2 ordered structure has been analyzed by using the anisotropic elasticity theory of dislocations and fracture. Screw superpartials cross slip easily at the boundary onto the (1$\overline 1$1) and the (001) planes at low and high temperatures, respectively. Transmission of primary slip dislocations onto the conjugate slip system occurs with a certain degree of difficulty, which is eased by localized disordering. When the transmission is impeded, cleavage fracture on the ($\overline 1$11) plane is predicted to occur, not intergranular fracture, unless a symmetric double pileup occurs simultaneously. Absorption (or emission) of superpartials occurs only when the boundary region is disordered. Slip initiation from pre-existing sources near the boundary can occur under the local stress concentration. Implications of the present result on the inherent brittleness of grain boundaries in Ni3 Al and its improvement by boron segregation are discussed.