it provides one of the few ways to control recrystallization by controlling the particle distribution. The size and misorientation of the deformed zone is related to the particle size and so there is a minimum particle size required to initiate nucleation. Increasing the extent of deformation will reduce the minimum particle size, leading to a PSN regime in size-deformation space. If the efficiency of PSN is one (i.e. each particle stimulates one nuclei), then the final grain size will be simply determined by the number of particles. Occasionally the efficiency can be greater than one if multiple nuclei form at each particle but this is uncommon. The efficiency will be less than one if the particles are close to the critical size and large fractions of small particles will actually prevent recrystallization rather than initiating it (see above). Bimodal particle distributions The recrystallization behavior of materials containing a wide distribution of particle sizes can be difficult to predict. This is compounded in alloys where the particles are thermally-unstable and may grow or dissolve with time. In various systems, abnormal grain growth may occur giving rise to unusually large crystallites growing at the expense of smaller ones. The situation is more simple in bimodal alloys which have two distinct particle populations. An example is Al-Si alloys where it has been shown that even in the presence of very large (<5 μm) particles the recrystallization behavior is dominated by the small particles (Chan & Humphreys 1984). In such cases the resulting microstructure tends to resemble one from an alloy with only small particles. Recrystallization Temperature The recrystallization temperature is temperature at which recrystallization can occur for a given material and processing conditions. This is not a set temperature and is dependent upon factors including the following: Increasing annealing time decreases recrystallization temperature Alloys have higher recrystallization temperatures than pure metals Increasing amount of cold work decreases recrystallization temperature Smaller cold-worked grain sizes decrease the recrystallization temperature See also Phase diagram References Metallurgy Phase transitions