Grain growth kinetics in alumina-rich, zirconia-alumina composites have been examined as a function of volume fraction of zirconia. Both the microstructural scale and character alter during grain growth. Grain growth exponents between n = 3 and 4 were observed and have been rationalized in terms of current models for grain growth and particle coarsening. Grain growth constants were measured and compared with available data. Coupled grain growth was observed in that the ratio of the alumina-to-zirconia grain size was constant, for a given zirconia content. This behavior is discussed in terms of the topological constraint present during growth and the observed microstructural evolution. The measured activation energies were consistent with boundary-diffusion-controlled grain growth.

Grain Growth Kinetics in Alumina–Zirconia (CeZTA) Composites

Second phases are used widely in the design of alloys. The state of enlightenment in their use is reviewed. Attention is paid to a) processes to insert second phases, b) design of second phase morphology, and c) the use of second phases to control grain structure (size, orientation, shape) and dislocation networks. Optimization of design for strength, ductility and toughness, fatigue resistance, stress corrosion cracking resistance and fabricability is treated.

alloy design,using second phases

Ti–3.5Al–5Mo–6V–3Cr–2Sn–0.5Fe is a high-strength β titanium alloy that shows excellent tensile properties. This paper presents the effect of hot rolling and heat treatment on the microstructure and tensile properties of this alloy. Microstructure observation shows that the α+β rolled alloy leads to smaller β grain size than the β rolled alloy in all heat treatment conditions. Solution treatment of the alloy in the α+β field can also lead to smaller β grain than solution in the β field. Tensile results indicated that the strength of the alloy was improved greatly by aging heat treatment, which was attributed to the secondary α phase. The 790 °C rolled alloy can obtain an ultimate strength of 1744 MPa by solution at 800 °C plus aging at 440 °C. The strength decreases and ductility increases with the increase of aging temperature. Moreover, the ductility of the alloy is significantly determined by the rolling and solution procedure. Rolling and solution treated at the α+β field results in better ductility than rolling and solution at the β field. Therefore, to obtain the high ductility, the α+β rolling and α+β solution should be chosen as long as possible before aging heat treatment.

Effect of hot rolling and heat treatment on microstructure and tensile properties of high strength beta titanium alloy sheets

The interface phase in alpha-beta titanium alloys

Bauschinger effect during cyclic straining of two ductile phase alloys

Methods of revealing grain size in a two-phase α-β titanium alloy have been examined and observations on beta grain growth in the presence of alpha have been carried out. The technique proposed by Greenfield and Margolin1 for revealing β matrix grain sizes has been shown not to produce grain growth. However, for grain sizes of about 10 µm the G.M. technique does not reveal all the grains because of the similarity in orientation in neighboring grains. These clusters of similarly oriented grains are shown to persist as grain growth takes place but the misorientation between grains within a cluster decreases. Both the beta grain growth and alpha particle coarsening follow the same time dependency from which it is shown that a linear relationship exists between α particle size and β grain size. It is proposed that α particles must dissolve from theβ grain edges for β grain growth to occur. The linear dependency between beta grain size,Dβ, and alpha particle size,dα, can be rationalized either on the basis of geometrical or surface tension considerations.

Grain size and grain growth in an equiaxed alpha-beta titanium alloy

: The investigation to relate fracture toughness, void formation and growth and ductility to microstructural features in an alpha-beta alloy, Ti-5.25Al-5.5V-0.9Fe-0.5Cu continued. New data confirm the earlier reported relationships between fracture toughness and microstructure of both equiaxed alpha and Widmanstatten plus grain boundary in aged beta matrix morphologies. In equiaxed alpha structures, fracture toughness depends linearly upon the grain boundary area per unit volume, S sub V, and is independent of equiaxed alpha particle size or spacing. In a grain boundary alpha structure, fracture toughness depends both on S sub V and, within limits, linearly on the thickness of the grain boundary alpha. Equations relating tensile void growth rates to microstructure for both morphologies have been derived. Tensile fracture is shown to be intergranular in nature and occurs when a critical crack length-stress relationship s satisfied. The amount of ductility achievable in a specimen depends upon the rate of void growth. If the growth rate is rapid, the crack reaches a critical size for fracture at a lower applied stress and strain and hence the ductility is less. A mechanism for void growth at alpha-beta interfaces is presented which accounts for the higher frequency of voids at 30-70 degrees to the tensile axis. An explanation is offered to the apparently contradictory behavior in which grain boundary alpha improved fracture toughness but lowers tensile ductility. (Author)

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Ira Greenhut

Papers

Grain size and grain growth in an equiaxed alpha-beta titanium alloy

Strengthening Mechanism of High Strength Titanium Alloys.