The influence of small (subgrain) misorientation interfaces on the mechanical behavior of metals and alloys deforming within the creep regime has been intensively studied over the past several decades. Controversies have existed, but some new experiments suggest, contrary to the general opinion, that low-angle boundaries are not associated with the rate controlling process for plasticity and do not affect strength. The new evidence will be discussed in terms of other established experimental trends. Large-angle boundaries may have a smaller effect on elevated temperature strength than at ambient temperatures and do not appear to dramatically affect elevated temperature strength. Superplastic effects are not addressed.

Nb base alloys with high Zr and C contents possess high strengths at up to 1400°C, but their low-temperature ductilities are unacceptably low due to nearly continuous rough eutectic carbide net along grain boundaries. The net has been broken by rapid solidification (RS). The structure and microhardness of these alloys after RS as well as after consequent compacting and/or annealing have been studied.

Preliminary results of a research aimed to identify the influence of the morphological characteristics of the grains constituting a quartz sand on the mechanical behaviour of the sand itself are presented. The tests were conducted on different size class samples resulting from a grain-size classification of the sand following the international standard classification (ASCII) procedure. For each sample traditional direct shear laboratory tests and an accurate characterisation of morphological and morphometrical properties of their constituting elements (grains) by means of digital image processing techniques were conducted. The statistical distribution of the different parameters derived following the two above mentioned procedures was studied and the results discussed.

Mass transport properties are important in polycrystalline materials used as protective films. Traditionally, such properties have been studied by examining model polycrystalline structures, such as a regular array of straight grain boundaries. However, these models do not account for a number of features of real grain ensembles, including the grain size distribution and variations in grain shape. In this study, a finite difference scheme is developed to study transient and steady-state mass transport through realistic two dimensional polycrystalline microstructures. Comparisons with the transport properties of traditional model microstructures provide regimes of applicability of such models. The effects of microstructural parameters such as average grain size are examined.

The effect of crystallographic texture and grain size on the cyclic hardening of FCC polycrystals was studied using copper as a model material. Samples with textures approximately random and two grain sizes were tested under cyclic loading. The cyclic response for high values of the plastic strain amplitude of the random-textured material was softer than that of polycrystals with strong <111>-<100> texture reported in [1], and almost the same at low plastic strains, when similar testing conditions were used. The cyclic behavior of specimens with different grain sizes and similar texture was almost the same as well. This result shows that texture had a much more important effect on the cyclic behavior of polycrystalline copper than the grain size. The effect of ramp loading as a pretreatment was also studied. The results show that large grained samples had a softer cyclic response after the ramp than small grained ones, but the effect was still smaller than that of texture.

We investigate a reaction rate of Mg-Li Al alloy (specific gravity is 0.95) in water. The hydrogen gas is mainly generated as follows : Li + H2O → LiOH + 1/2 H2 ↑. Using the volume of hydrogen gas, the reaction rate is estimated. The apparent activation energy (E) is 4.63 kcal/mol for the early reaction period. It is approximately equal to that of the water diffusion. On the other hand, the E is 9 kcal/mol after the early reaction period at the 2 ml (the volume of hydrogen gas). Furthermore, we succeed to prevent the sample against the reaction by the use of coating paints.

Image analysis and measurements on forimation and spatial statistics of spherulitic grain pattern in solidified films of a model polymer, isotactic polypropylene (iPP), have been carried out during in-situ observation experiments under isothermnl conditions. Topological correlations and geometrical distribution fuinctions of polymer grain sides and area are reported. Some topologically unstable configurations, such as multi-vertices, “T” type vertices and two sided grain (lens), have been found. Analysis by spatial tessellations shows that the tenWal evolution and spatial distributions of nuclei point patterns play a role in all of these microstructural properties.

The influence of grain size on corrosion fatigue behavior of A537 steel in 0.1M HCL solution has been studied. The results show that the increase of grain size can improve the corrosion fatigue crack growth resistance. But the change of crack growth rate da/dN with average grain diameter D is not monotonic. When D>40 μm, crack propagates little faster when grain is larger. When D>40 μm, crack propagates slower when grain is larger. According to the fractographic features, corrosion fatigue mechanism is anodic dissolution under fine grain condition but hydrogen embrittlement under coarse grain condition.

Ti6AI4V rings have been centrifugally spray deposited with the long term aim of producing sheet which can be superplastically formed. Spray deposition has been carried out under vacuum and under an argon atmosphere in order to assess the significance of gas entrapment during spray forming. Some samples have been HIPped and others have been used for hot rolling trials after spray deposition and the microstructures of these differently treated samples compared. Some preliminary measurements of the room temperature tensile properties have also been made.

The results are briefly discussed in terms of the advantages of using a vacuum spray forming route and in terms of the properties of the spray-formed and HIPped samples.

Microstructure of rapidly solidified Cu-5wt%Nb ribbons produced by melt spinning was investigated by SEM and TEM techniques. Two heat treatments were done: 960°C 1 hour and 900° 3 hours. The microstructures contained three different type particles: (a)large particles located at the grain boundary, (b)small spherical particles located within the grains and at the grain boundaries, and (c)fine precipitates formed upon heat treatment. The evolution of the microstructure is discussed with regard to the previously reported studies.

It has become possible in recent years to synthesize metals and ceramics under well controlled conditions with constituent grain structures on a nanometer size scale (below 100 nm). These new materials have mechanical properties that are strongly grain-size dependent and often significantly different than those of their coarser grained counterparts. Nanophase metals tend to become stronger and ceramics are more easily deformed as grain size is reduced. The observed mechanical property changes appear to be related primarily to grain size limitations and the large percentage of atoms in grain boundary environments. A brief overview of our present knowledge about the grain-size dependent mechanical properties of nanophase materials is presented.

Thin copper foils (100 micrometers thick) are produced by electrolysis on anodized titanium substrates. A sharp distribution of grain diameter is observed around 200 nanometers. The X-ray diffraction pattern shows a slight preferential orientation of the crystals with the (111) planes parallel to the substrate. This X-ray diffraction pattern evolves at room temperature. After 60 days, a preferential orientation of the (200) planes parallel to the substrate is observed. This effect is associated with the recrystallisation of the foil with growth of large copper grains (diameter higher than 5 micrometers) as observed by high resolution transmission electron microscopy.

The structural evolution of the copper foils is studied by electron microscopy, X-ray and electron diffractions at different temperatures.

The mechanical properties of the foils are also studied as a function of time after electrodeposition.

Zr-, Al-, and Mg-base transition metal alloys have been prepared by mechanical alloying and investigated by x-ray diffraction, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). Amorphous phases with significant supercooled liquid region form directly during milling from the crystalline starting materials for Zr- and Mg-base alloys. For Albase alloys the formation of mixtures of amorphous and nanocrystalline phases is observed. The results are compared with data for melt-spun and quenched materials. Possible mechanisms for glass formation and crystallization are discussed.

This work reports on the mechanical properties of nanocrystalline NiAI materials. Mechanically- milled NiAl with and without Al2O3 additions was forged to 94% of the theoretical density of stoicheometric NiAl at < 0.5 Tm in air. Mechanical properties were investigated by microhardness measurements and the Miniaturized Disk-Bend Test (MDBT). Analysis of the hardness data indicates that most of the compression strengthening is due to the refined microstructure. MDBT results are consistent with tensile tests indicating that the tensile strength is controlled by the strength of grain boundaries.

The use of mechanical hardness as a probe of nanocrystalline materials is reviewed. The fact that the grain size dependence of hardness is very different for nanocrystalline materials compared to conventional (≥1 μm diameter) polycrystals suggests a different deformation mechanism may be operative in nanocrystalline materials. Hardness is useful for following the sintering, densification reactions of nanoparticles. Solid solution hardening in nanocrystalline alloys is found to be overwhelmed by the grain boundary hardening. If alloying decreases the grain boundary hardening, i.e. increases grain size, an apparent solid solution softening effect is observed.

The purpose of the present work is to toughen the grain boundary phase of Si3N4 ceramics by forming a nano composite grain boundary phase of SiC particles. The nano SiC particles form through a reaction between the coated carbon and the surface oxidation phase in Si3N4. The carbon is coated through thermal decomposition of CH4 gas. The sintcred bodies arc obtained by hot-pressing at 1800 °C for one h. By increasing the carbon content, both fracture toughness and bending strength initially increase, then reach the maximum value at the same amount of carbon content, and decrease. The carbon content at which the fracture toughness and bending strength exhibit the maximum value increases with the increase in the surface oxygen content. The precipitated SiC particles dispersed in a grain boundary phase, at a Si3N4-Si3N4 interface or in a Si3N4 grain. The locations and size (less than 30 nm) of the SiC particles are examined by TEM and HREM observations. As the grain boundary is toughened by the precipitated nano SiC particles in the grain boundary phase or at the Si3N4-Si3N4 interface to help Si3N4 grain bridging without any glassy phase, these SiC particles block or resist the intergranular fracture.

A Monte Carlo simulation procedure is applied to simulate non-uniform grain growth during directional annealing. The assumed temperature profile consists of a small, finite size hot zone which blends smoothly into cold zones ahead and behind the hot zone. The hot zone is assumed to move with a constant velocity. The influence of the ratio of hot zone to cold zone temperatures and the velocity of the temperature field are investigated. The grain size is analyzed as a function of these variables. We find that very high aspect ratio grains (long axis parallel to the thermal field velocity vector) are possible within a restricted velocity window. These results are analyzed in terms of an analytic model based upon conventional grain growth laws.