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Chapter 16: Problem 5

Cite one similarity and two differences between precipitation hardening and dispersion strengthening.

Short Answer

Expert verified
Answer: The similarity between precipitation hardening and dispersion strengthening is that both processes strengthen materials by obstructing dislocation motion through the presence of fine precipitates or dispersed particles within the matrix. The first difference between the two processes is the nature and origin of the strengthening particles, with precipitation hardening involving precipitates formed from the material's alloying elements, while dispersion strengthening involves particles incorporated from an external source. The second difference lies in their applicability to different materials, with precipitation hardening suitable for specific alloy systems and dispersion strengthening applicable to a broader range of materials, including metals, alloys, ceramics, and composites.

Step by step solution

01

Define Precipitation Hardening

Precipitation hardening is a heat treatment process that is used to strengthen certain alloys by inducing the formation of very fine, uniformly distributed precipitates within the alloy's matrix. It involves three main steps: solutionizing, quenching, and aging. During solutionizing, the alloy is heated to dissolve the alloying elements, followed by rapid cooling (quenching) to retain a supersaturated solid solution. Then, during the aging process, the alloy is kept at an elevated temperature to allow the precipitation of the second phase, creating fine precipitates that act as obstacles to dislocation motion, ultimately strengthening the material.
02

Define Dispersion Strengthening

Dispersion strengthening is another technique used to improve the mechanical properties of materials, particularly metals and alloys. The process involves the incorporation of finely dispersed, hard, and thermally stable particles into a matrix. These dispersed particles act as obstacles and obstruct the dislocation motion in the material, resulting in an increase in its strength. The particles can be introduced into the matrix either during the material's fabrication process (by powder metallurgy or melt processing) or by in-situ precipitation.
03

Identify the Similarity

The similarity between precipitation hardening and dispersion strengthening lies in their primary strengthening mechanism, which involves obstructing the movement of dislocations in the material. In both processes, the presence of fine precipitates or dispersed particles within the matrix hinders dislocation motion, leading to an increase in the material's strength and resistance to deformation.
04

Explain the First Difference

The first major difference between precipitation hardening and dispersion strengthening is the nature and origin of the strengthening particles. In precipitation hardening, the particles (precipitates) are formed from the alloying elements within the material itself during the heat treatment process. In contrast, in dispersion strengthening, the particles are incorporated into the material from an external source and are typically made of a different material than the matrix.
05

Explain the Second Difference

The second major difference between these processes is their applicability to the types of materials they can strengthen. Precipitation hardening is suitable for specific alloy systems, such as aluminum, copper, and certain stainless steels. This process relies on the alloy's specific composition and reaction to heat treatment to form the precipitates. Dispersion strengthening, on the other hand, can be applied to a broader range of materials, including metals, alloys, ceramics, and composites, as its strengthening mechanism depends on the presence of uniformly distributed, hard, and thermally stable particles within the matrix, regardless of the material's composition.

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Most popular questions from this chapter

(a) What is the distinction between matrix and dispersed phases in a composite material? (b) Contrast the mechanical characteristics of matrix and dispersed phases for fiber reinforced composites.

(a) Write an expression for the modulus of elasticity for a hybrid composite in which all fibers of both types are oriented in the same direction. (b) Using this expression, compute the longitudinal modulus of elasticity of a hybrid composite consisting of aramid and glass fibers in volume fractions of 0.25 and 0.35 respectively, within a polyester resin matrix \(\left[E_{m}=4.0 \mathrm{GPa}\left(6 \times 10^{5} \mathrm{psi}\right)\right]\)

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