Solid Solution, Second-phase, and deformation are three common TZM strengthening mechanisms. While related to some extent, these three TZM (titanium-zirconium-molybdenum) strengthening mechanisms have some differences in principle and effect.
Solid Solution Strengthening Mechanisms
The solid solution in TZM alloy mainly refers to the solid solutions formed by adding titanium, zirconium, and other elements into molybdenum. The elements are dissolved with molybdenum grains, significantly improving the mechanical properties of the resulting alloy.
There are several common types of TZM solid solutions:
Titanium solid solution: This solid solution of titanium and molybdenum increases the strength and toughness of TZM, thus extending durability and service life of the alloy.
Zirconium solid solution: Zirconium can also form a solid solution with molybdenum, which improves corrosion resistance and high-temperature performance of the resulting alloy. This makes it suitable for use in high-temperature, high-pressure, and strongly corrosive environments.
Titanium-zirconium dual solid solution: The dual solid solution of titanium and zirconium with molybdenum can enhance both strength and toughness of the molybdenum grains, thereby improving the mechanical properties of the alloy.
The crystallization structure and distribution of the various solid solutions can be regulated by controlling their composition and sintering processes to achieve better strengthening effects, corrosion resistance, high-temperature performance, and other critical performance attributes.
Second-phase Strengthening Mechanisms
The other main TZM strengthening mechanism is the addition of so-called “second-phase” particles that form high-density interfaces with molybdenum grains. This hinders movement of grain boundaries and limits the growth of grains within the alloy. Second-phase strengthening can significantly improve the strength and toughness of TZM alloy.
Second phase particles in the TZM alloy may include various compounds, including:
Compounds of titanium and zirconium: Titanium and zirconium have a strong chemical affinity with molybdenum, allowing them to form the second phase of molybdenum-based alloys. Among the common second phase compounds are titanium-molybdenum (TiMo2, Ti2Mo, Ti5Mo3, etc.); and zirconium-molybdenum, (ZrMo2, Zr2Mo, Zr5Mo3, etc.)
Carbides: Carbides are another group of common second-phase particles in TZM alloy. These are usually formed by the reaction of carbon elements with the other metals, e.g. molybdenum carbides such as Mo2C, MoC and titanium carbides such as TiC.
Deformation Strengthening Mechanism
The TZM alloy can experience deformation TZM strengthening at recrystallization temperatures, and the effectiveness of this TZM strengthening increases with greater amounts of deformation. Methods of deformation strengthening include forging, extrusion, and hot rolling. During the deformation process, the alloy’s grains stretch along the processing direction, leading to lattice distortion, a higher dislocation density, and the emergence of secondary, refined grains. This results in improved alloy strength.