The Allotropic Transformation of Hafnium

The existence of an allotropic transformation in hafnium, suggested by Zwikker in 1926, has been confirmed. The transformation temperature is 1310±10°C. The high temperature beta-form is probably body-centered cubic

Amorphous Phase in Palladium—Silicon Alloys

By rapid cooling from the melt, an amorphous phase has been obtained in palladium—silicon alloys containing 15 to 23 at.% Si. This phase is stable at room temperature and crystallization cannot be detected after one month at 250°C. With rates of heating greater than 20°C/min, rapid crystallization takes place at 400°C, with a heat release of approximately 1000 cal/mole. The electrical resistivity of an alloy containing 17 at.% Si at room temperature is 2.6 times that of the equilibrium alloy. The resistivity decreases linearly with decreasing temperature and is about 95% of the room-temperature value at 2°K. Various factors involved in the retention of amorphous phases in rapidly quenched liquid alloys are discussed

Metastable Electron Compound in Ag-Ge Alloys

Abstract unavailable

Metastable Solid Solutions in the Gallium Antimonide-Germanium Pseudobinary System

Abstract unavailable

Metastable amorphous phases in tellurium-base alloys

An amorphous structure has been reported in a gold-silicon alloy (2) obtained by rapid cooling through the solidification range.(3) This amorphous alloy, however, was not stable at room temperature. Crystallization into one or several metastable phases took place within twenty-four hours, and a detailed study of the structure could not easily be carried out

Metastable amorphous ferromagnetic phases in palladium-base alloys

The existence of an amorphous phase obtained by rapid quenching from the liquid state, has been recently reported in palladium alloys containing from 16 to 22 at % silicon.(1) Since the ferromagnetic elements iron, cobalt, and nickel, form complete series of solid solutions with palladium, it was anticipated that the amorphous structure could be retained if these elements were substituted for palladium up to a certain concentration

A typical example of metastability: Metallic glasses

The general term metallic glasses is now generally accepted to define a class of amorphous alloys obtained by rapid solidification from the liquid state. This definition corresponds exactly to the definition of a glass in general, except that in the case of well known silicate glasses the liquid does not require a rapid rate of cooling to prevent crystallization, and that is not the case for metallic glasses. The first metallic glass, an alloy of gold and silicon, was synthesized at Caltech in the summer of 1959. During the last 20 years, the interest in metallic glasses has increased steadily. There is still widespread interest in both theoretical and experimental studies of metallic glasses. About 10 years ago the potential importance of metallic glasses as a class of new materials with unusual physical properties was recognized by industry. It will take a long time before production of metallic glasses can be measured in tons, but it is encouraging to see that an increasing number of industrial research centers are involved in studies of metallic glasses

On the Plasticity of Crystals

In the following, a theory is given with the purpose of establishing a mathematical relation between the stress and the strain in a crystal when plastically deformed. The existence of a "secondary structure" in crystals is adopted as a basic hypothesis. This structure was pointed out by Professor F. Zwicky to be a consequence of what he calls "cooperative phenomena." The assumption that gliding in crystals takes place between the blocks of the secondary structure is the starting point of the following theory. The additional hypothesis of assuming a statistical distribution of the different forces which produce gliding between the blocks, gives us the means for going further in the calculations. The final result which is the stress strain curve of a crystal, is an exponential law containing three constants, i.e., the torsional modulus G, the elastic limit, (γs,τs) and the maximum applicable stress τm. The form of the hysteresis cycles is deduced from the same considerations and moreover a formula is obtained for the areas of the cycles. Experimental verifications were made on a single crystal of copper, and also on ordinary microcrystalline copper

The Effect of the Rate of Cooling on the Allotropic Transformation Temperatures of Uranium

Allotropic transformation in uranium has been studied over a range of cooling rates from 5 to about 8000°C/sec. The transformation temperatures of both gamma‐to‐beta and beta‐to‐alpha were found to decrease continuously with increasing rates of cooling. The extent of the beta‐range increased with increasing cooling rates. For rates of cooling up to 1000°C/sec, recalescence was observed in both transformations. For higher cooling rates, there was usually no recalescence. In most of the recorded cooling curves, a small but definite thermal arrest was observed, between the two main arrests which correspond to the two known phase transformations. This additional thermal arrest was also present in a heating curve, where it occurred at about 740°C, compared with 666 and 771°C for the two known phase transformations. Possible explanations of the additional arrest are discussed