Ageing after Quenching

Chapter II. Quenching—Quenching Temperature, Rate of Cooling, and Ageing after Quenching. 

A typical application is the detection of sub-boundaries in Al-Zn solid solutions with enough Zn to allow precipitation-hardening at room temperature after quenching. During such aging, Zn atoms concentrate at the sub-boundary dislocation walls to a sufficient extent to cause a color variation of the... 

Fig. 1. Polygonization sub-boundaries in a solid solution Al-Zn after quenching and aging at room temperature thin anodic film with interference tints (18).

So far, the phenomena discussed pertain to isothermal ageing after a quench (rapid cooling) from above to below Tg. Under such circumstances, ageing always runs in the same direction (increasing retardation times). Peculiar phenomena occur, however, when after a period of ageing at temperature T, the material is heated to a final temperature between T and Tg T < Too < Tg). A good example is poly(vinyl chloride) (PVC) with Tg 80 °C. Struik (1978) compared two samples for which the ageing times at T = 20 °C differ by a factor of 18. When tested at 20 °C, their creep properties differed considerably, but all differences disappeared when the tests were done at 50 °C. 

Figure 3.5 shows the temperature variation of H for the four above mentioned polymers, namely PMMA, PVAc, PET and PEEK. In the case of the two amorphous polymers (PMMA and PVAc) H decreases with T and the Tg value can he clearly identified with a hend in the 7/ vs T plot. However, the two semicrystalline materials quenched into the amorphous state (PET and PEEK) show an apparent maximum just before the glass transition takes place. Also, in the case of PET tested immediately after quenching it is observed that H increases with T above room temperature. These phenomena will be discussed in Section 3.3 in the light of the physical ageing undergone by the above polymers. It is seen that H follows an exponential decrease as a function of T given by (see eq. (2.5))... 

There is a slight difference between freshly molded samples and aged samples in swelling behavior. The freshly molded samples approached equilibrium somewhat faster but it was not noted in very short time measurements, except for 303-50 as indicated in Table 1. It is likely, therefore, that interactions between zinc stearate and sulfonate moieties develop rather rapidly after quenching the... 

And] Optical micrography, Brinell hardness Room temperature after quenching at 100°C ad ageing at 610-820°C, 0.05 - 1.51 mass% Si, 2.28 - 57.28 mass% Cr... 

The origin of physical ageing in an amorphous polymer. After quenching to a temperature below Tg (but above T, the temperature of the highest secondary relaxation), the volume stCM4y contracts the movement is towards the equilibrium, which is the extrapolMed V - T line for the liquid (after Struik). 

Excess Ageing after a Temperature Quench Following Previous Ageing at Higher Temperatures... 

M. Aboulfaraj, C. G Sell, D. Mangelinck, and G. B. McKenna, Physical Aging of Epoxy Networks after Quenching and/or Plastic Cycling , J. Non-Cryst. Solids 172-174, 615-621 (1994). 

---