PRECIPITATION IN /cap beta/ TITANIUM-VANADIUM ALLOYS

Journal Article · Sun Oct 01 04:00:00 EDT 1961 · Z. Metallk.

OSTI ID:4802271

Krisement, O

The tempering of beta Ti-V alloys occurs in two steps. Cold hardening is observed from room temperature up to 400 deg C, and above 400 deg C the precipitation of the hexagonal alpha equilibrium phase occurs simultaneously with cold hardening. To compare microcalorimetric measurements of the precipitation processes with thermodynamic data, the heat of mixing of beta alloys was calculated from the ( alpha + beta ) phase boundaries. A positive heat of mixing is found, thus indicating the existence of a mixing gap which has not yet been observed experimentally. For the investigated alloys with 14.7 to 19.1 at.% V, the upper temperature limit for cold hardening was found to be T/sub K/ = 475 deg C. This temperature is very probably determined by the position of the spinodal curve. In the cold hardening region the appearance of the metastable omega phase is observed, which could be proved with the neutron diffraction pattern. The isothermal kinetics of cold hardening, measured with the heat release Q(t) per unit of time, is governed by a hyperbolic law, and the total amounts of heat given off are very close to those which are to be expected when the alloy is decomposed according to the calculated mixing gap. The diffusion process acting during cold hardcning could not be analyzed: its activation energy must be significantly smaller than the activation energy of the chemical diffusion coefficient for titanium and vanadium, though not much excess quenched-in vacancies could be present. The latter activation energy was determined from the temperature dependence of the alpha phase precipitation in the second tempering stage which gave the value A = 55,000 cal/mole. D/sub o/ was found to be approximately 5 cm/sup 2//sec. The alpha phase is precipitated by nucleation and diffusion-controlled growth, and nucleation occurs very probably in a homogeneous manner. The heat given off during precipitation is about the same as calculated from the decomposition of the initial beta crystals in domains of different vanadium content given by the ( alpha + beta ) boundaries, the heat of beta - alpha transformation thus being small in the temperature range from 400 to 450 deg C in comparison to the heat of mixing of the beta alloys. (auth)

• Research Organization: Max-Planck-Institut fur Eisenforschung, Dusseldorf
• NSA Number: NSA-16-010600
• OSTI ID: 4802271
• Journal Information: Z. Metallk., Journal Name: Z. Metallk. Vol. Vol: 52
• Country of Publication: Country unknown/Code not available
• Language: German

Related Subjects

ACTIVATION ENERGY
ALLOTROPY
CALORIMETERS
COLD WORKING
CONTROL
CRYSTALLIZATION
CRYSTALS
DECOMPOSITION
DEFECTS
DIFFRACTION
DIFFUSION
EXCITATION
EXPANSION
GRAIN BOUNDARIES
HARDNESS
HEAT TRANSFER
HEAT TREATMENTS
LATTICES
LOW TEMPERATURE
MATHEMATICS
MEASURED VALUES
METALS, CERAMICS, AND OTHER MATERIALS
MIXING
MIXING HEAT
NEUTRON BEAMS
NUCLEATE BOILING
PHASE DIAGRAMS
PRECIPITATION
QUANTITY RATIO
QUENCHING
REACTION KINETICS
SPECIFIC HEAT
STABILITY
TEMPERATURE
TEMPERING
THERMODYNAMICS
TITANIUM
TITANIUM ALLOYS
TITANIUM- BETA
TRANSFORMATION HEAT
VACANCIES
VANADIUM
VANADIUM ALLOYS