Titanium alloys have been used extensively in the aerospace, structural and power industries due to their attractive combination of physical and mechanical properties. It is widely understood that these properties depend closely upon the microstructure of the alloy. This microstructure is in turn formed during the thermomechanical processing of the alloys. It is therefore desirable to know the effect of different processing routes on the microstructure of the alloy so that the required mechanical properties can be achieved.

In this work the mechanical properties of a typical α alloy, Ti-6Al-4V, and a typical β alloy, β21s, are determined after appropriate heat treatment. The α alloy is heated into the 100% β phase field (1100ºC) and then cooled at six different rates (5-50ºC/min). The β alloy is solution treated at 810ºC and then aged at three different temperatures (480-595ºC) for 8 hours.

The microstructure after heat treatment is studied by optical microscopy for both alloys. Mechanical testing consists of tensile testing (room and elevated temperatures), impact testing and hardness testing.

            Ti-6Al-4V forms a fully lamellar microstructure on cooling from the β phase field. Increasing the cooling rate leads to refinement of the lamellar spacing.  The faster cooling rates result in a stronger material, as the slip length of the alloy is related to the lamellar width.

            The aging of β21s is results in the precipitation of α, which causes strengthening. The amount of precipitation is related to the degree of under-cooling of the alloy. Beta grain size also affects the ductility of the material

            Recommendations are given for the optimum processing route for desirable mechanical properties.

Titanium alloys have been used extensively in the aerospace, structural and power industries due to their attractive combination of physical and mechanical properties. It is widely understood that these properties depend closely upon the microstructure of the alloy. This microstructure is in turn formed during the thermomechanical processing of the alloys. It is therefore desirable to know the effect of different processing routes on the microstructure of the alloy so that the required mechanical properties can be achieved.

In this work the mechanical properties of a typical α alloy, Ti-6Al-4V, and a typical β alloy, β21s, are determined after appropriate heat treatment. The α alloy is heated into the 100% β phase field (1100ºC) and then cooled at six different rates (5-50ºC/min). The β alloy is solution treated at 810ºC and then aged at three different temperatures (480-595ºC) for 8 hours.

The microstructure after heat treatment is studied by optical microscopy for both alloys. Mechanical testing consists of tensile testing (room and elevated temperatures), impact testing and hardness testing.

            Ti-6Al-4V forms a fully lamellar microstructure on cooling from the β phase field. Increasing the cooling rate leads to refinement of the lamellar spacing.  The faster cooling rates result in a stronger material, as the slip length of the alloy is related to the lamellar width.

            The aging of β21s is results in the precipitation of α, which causes strengthening. The amount of precipitation is related to the degree of under-cooling of the alloy. Beta grain size also affects the ductility of the material

            Recommendations are given for the optimum processing route for desirable mechanical properties.

Effect of heat treatment on the microstructure and mechanical properties of titanium alloys

Titanium alloys have been used extensively in the aerospace, structural and power industries due to their attractive combination of properties. It is widely understood that these properties depend closely upon the microstructure of the alloy. This microstructure is formed during the thermomechanical processing of the alloys . It is therefore desirable to know the effect of different processing routes on the microstructure of the alloy so that the required mechanical properties can be achieved.

In this work the mechanical properties of a typical α alloy, Ti-6Al-4V, and a typical β alloy,  β21s,  are determined after appropriate heat treatment. The α alloy is heated into the β phase field (1100ºC) and then cooled at varying rates (5-50ºC/min) [Fig. 1]. The β alloy is solution treated at 810ºC and then aged at different temperatures (480-595ºC) for the same length of time [Fig. 2].

The microstructure after heat treatment was studied by optical microscopy. Mechanical testing consisted of tensile testing (room and elevated temperatures), impact testing  and hardness testing.

            Ti-6Al-4V forms a fully lamellar microstructure on cooling from the β phase field [Fig. 3]. Increasing the cooling rate leads to refinement of the lamellar spacing [Fig. 4].  It is expected that the faster cooling rates will result in a stronger material, as the slip length of the alloy is related to the lamellar width.

            The aging of β21s is expected to result in the precipitation of α, which causes strengthening. It is expected that the amount of precipitation will be related to the degree of undercooling of the alloy.

            Recommendations will be given for the optimum processing route for required properties.