Rheology
Forming at the semi-solid state - Rheoforming and thixoforming

Right from the start, rheological properties of alloys during solidification were determined using a Couette-type viscometer. Its advantage is that the globular-structured alloy can be obtained directly in the device. During the test, the alloy is sheared between two concentric cylinders, the inner one fixed and the outer one rotating at a constant angular speed.

A fixed outer cylinder and a rotating inner cylinder define a Searle viscometer. The torque required to shear the alloy is continuously recorded. From angular velocity and torque, it is possible to deduce shear rate and shear stress, subject to certain simplifying assumptions. The test is then easy to perform, but problems arise when very clean experiments...