Systems Containing Four Phases

Abstract

An invariant reaction in a ternary system occurs when four phases co-exist in equilibrium. Two forms of such reaction will be discussed, each involving a liquid (L) and three solid phases (primary solid solutions) ±, β,and γ

• 1. A ternary eutectic reaction L; →α + #x03B2; + γ

• 2. A ternary peritectic reaction type (a); L; + α → #x03B2; + γ type (b);L; + α+ → #x03B2;→ γ

In some accounts the designation 'peritectic' is restricted to the type (b); reaction, and type (a); is viewed as being intermediate in nature between eutectic and peritectic. However, in the present account, the term 'peritectic'is applied to both these types.