Effect Of Dispersoids Research Articles

The effect of dispersoids on the ductile fracture toughness of AlMgSi alloys

Abstract The ductile fracture toughness J Ic of AlMgSi alloys aged to peak hardness is measured as a function of dispersoid volume fraction. It is found that the toughness increases with dispersoid content, for alloys having similar grain sizes and yield strengths, and this increase is attributed to the homogenization of slip distribution. The crack tip plastic zone sizes are determined experimentally as a function of applied stress intensity factor K and a model, based on the crack tip blunting geometry, is proposed to explain the variation in zone size with dispersoid content. A relationship between fracture toughness J Ic and the work per unit area of new fracture surface, dW/dA, bears out the contention that the increased toughness caused by an increased amount of dispersoid particles is due to finer spread-out slip at the crack tip.

Creep of dispersion-strengthened alloys

Abstract The importance of dispersed second-phase particles in providing strengthening of alloys both at room temperature and at high temperatures has long been recognized and the effects of dispersoids have been the subject of many research studies. These studies have led to a considerable understanding of the role of particles but inconsistencies still remain both in the experimental observations and in the interpretation of these observations. The purpose of this review is to examine the characteristics of high temperature creep of dispersion-strengthened alloys from the viewpoint of the possible mechanism involved. Three mechanisms of plastic deformation are distinguished and discussed. Specifically, these are examined in relation to oxide-dispersion-strengthened nickel-based alloys as these have potentially good high temperature corrosion resistance and useful creep resistance to high fractions of their melting points. These attractive properties at temperatures in excess of about 1000°C, where the useful creep strength of creep-resisting steels and superalloys rapidly diminishes, offer what at present appears to be the most technologically feasible development of materials for engineering applications at temperatures of 1100°C and above.

The effects of dispersoids upon the micromechanisms of crack propagation in AlMgSi alloys

Abstract The effect of dispersoids containing Mn or Cr. in a series of peak-aged AlMgSi alloys, upon the crack-tip plastic zone size has been studied by the use of Selected Area Channelling Patterns (SACPs). In the absence of such dispersoids. the alloy fractures in a brittle intergranular fashion; when the particles are present, the alloys are ductile but still fracture in a predominantly intergranular manner but with an increase in the size of the plastic zone associated with the crack tip. It is suggested that the toughening effect of the dispersoid phase is indirect through its effect upon the matrix grain size and upon the distribution of slip. Fracture occurs because slip bands impinge on grain boundaries, causing a local strain concentration which at some critical value nucleates a void, thereby causing an increment of crack extension.

Effect of Dispersoids on Magnetic Properties of Iron, Cobalt, and Nickel

Coercive force and saturation induction of cobalt, iron, and nickel, dispersion strengthened with 0.02 to 0.10 volume fraction of alumina or thoria, were measured at temperatures up to 80%–98% of TC. Saturation magnetization values of iron and cobalt at a given temperature level were found to decrease in direct proportion to the volume fraction of nonmagnetic phase present. The temperature dependence of the measured coercive force was interpreted as a cooperative effect of inclusions and internal stress by reference to coercive force values calculated from the equations of Néel. This was particularly apparent in the Hc vs T curve of nickel where the contribution of inclusions was significant in the low-temperature region, whereas stress was an influential factor at all temperatures. Close correlation between measured and calculated Hc was obtained for all three metals containing 0.02–0.025 volume fraction of dispersoid.