Precipitation Hardening Response Research Articles

High temperature precipitation hardening in a rapidly quenched Al [sbnd]Ti [sbnd]Ni alloy II. Precipitate characterisation

Changes in the morphology and structure of second phase particles, formed during isothermal ageing of rapidly quenched Al 6Ti 1.5Ni (wt.%) alloy at temperatures in the range 300–500°C, have been examined using a combination of conventional amplitude contrast imaging and electron microdiffraction. The precipitation-hardening response is initially attributable to a fine-scale distribution of coherent particles of metastable L1 2 phase and the orientation relationship between the metastable precipitate and α-aluminium matrix is such that (001) L1 2 //(001) α , [100] L1 2 //[100] α . During isothermal ageing, the metastable precipitates evolve with a transitional, three-dimensional cross-like morphology defined by three orthogonal sets of ellipsoidal elements forming in pairs. The precipitates comprise variants of a series of one-dimensional tetragonal superlattices that vary in structure from L1 2 to body-centred tetragonal D0 23; the c axis of the tetragonal cells is parallel to the major axis of each ellipsoidal segment and the orientation relationship is such that the principal axes of the ordered product superlattices are parallel to those of the matrix phase. The structural transformation from metastable L1 2 to equilibrium D0 22 phase, via an intermediate D0 23 structure can be modelled assuming aperiodic shear displacements of 1/2[110](001) within one-dimensional clusters of L1 2 unit cells, to create a range of one-dimensional tetragonal superlattices with differing c parameters.

Effects of Si Additions on the Precipitation Hardening Response in Al-Cu-Mg(-Ag) Alloys

Effects of Si Additions on the Precipitation Hardening Response in Al-Cu-Mg(-Ag) Alloys

Mechanical properties and precipitation-hardening response in ASTM A710 Grade A and A736 alloy steel plates

Addition of 1.0/1.3 pct copper has been used for precipitation hardening in a lowalloy steel containing less than 0.07 pct C, 0.40/0.70 pct Mn, 0.6010.90 pct Cr, 0.70/1.0 pct Ni, 0.15/0.25 pct Mo, and at least 0.02 pct Nb. This steel is included in ASTM Specifications as A710 Grade A for structural plates and as A736 for pressure vessel plates. A variety of strength and toughness combinations are provided by the selection of Class 1, Class 2, and Class 3 heat treatments.

Effect of composition on the properties of strain-transformable β titanium alloys

A number of metastableβ titanium alloys were examined to determine the effects of composition on strain-transformation behavior and precipitation hardening response. Maximum ductility as solution heat treated was observed in alloys slightly richer in alloy content than the minimum alloy content required to retain an all-β microstructure on quenching. Such materials transformed to a martensitic structure upon straining and, as a result of strain transformation, developed room temperature ductility exceeding that found in unalloyed titanium. Uniform elongation of 35 to 45 pct was observed in a number of compositions of this type containing major additions of Mo, V, Cr, or Mn. Auxiliary alloy additions of Sn, Al, or Zr, or ternary alloying with molybdenum were necessary to preventω embrittlement during quenching in alloys containing V, Cr, or Mn. Alloying with Fe, Cu, Co, or Ni resulted in low ductility as solution heat treated, but it is probable that optimum amounts of these additions were not studied in this investigation. Oxygen above about 1200 ppm also had a detrimental effect on ductility. All alloys studied showed precipitation hardening when heat treated in the 800° to 1100°F range. Tensile strengths of 170 to 190 ksi were readily attainable in most alloy systems. Ductility as precipitation hardened appeared to be higher in alloys containing at least 6 pct Mo or V than in other alloys studied.