TZM Rod Forging-Strength and Plasticity Deformation Optimized Process

TZM rod, titanium, zirconium, and molybdenum sintered alloy rod, has a high melting point, physical strength, erosion resistance, and other excellent high-temperature properties. Therefore, molybdenum alloy is commonly used in applications that need high-temperature resistance.

Powders of high purity titanium, zirconium, carbon, and molybdenum undergo several powder metallurgy processes, including mixing, isostatic pressing, and sintering, to transform to basic flat or round TZM compact. Further TZM compact rolling and annealing processes at designated temperatures yield the final shapes of TZM materials, such as TZM rods, sheets, or plates.

Optimizing TZM’s composite contents or deforming process can improve TZM materials’ physical strength and plastic deformation. For example, 0.30% to 0.65% of Hafnium (Hf) addition creates a bi-directional crystallite structure in TZM, while the multidirectional forge generates an isometric crystallite structure. These unique structures substantially increase TZM’s physical strength and deformation capacity.

 

TZM Rod Producing Process in More Detail

The TZM rod manufacturing process involves four major steps: powder compressing, powder sintering, rod forging, and heat treatment.

TZM rod isostatic pressing

Powders of titanium (0.5%), zirconium (0.08%), hafnium (0.5%), and carbon (0.02%) are mixed with molybdenum powder for balance. Hot isostatic pressing equipment condenses the mix for 1 to 2 hrs to turn powders into rod shapes. The pressing temperature is from 730 to 1550℃, and the pressing pressure is 170 to 280 MPa.

TZM rod sintering

The sintering process of TZM rods operates in two gas environments, vacuum, and inert gas. The sintering in each gas environment works at a specific heating gradient temperature: 1450–1700℃ in a vacuum and 1900–2250℃ in hydrogen. Vacuum sintering processes TZM rod for 1 to 2 h, and then inert gases, for example, argon gas, is refilled in the furnace for sintering for the next 5 to 7 h.

TZM rod multidirectional hot forging

The range of forging temperatures has to be controlled between 960℃ and1450℃, as higher temperatures may melt the molybdenum. In contrast, low temperatures may increase TZM’s hardness and cause breaking issues.

TZM rod heat treatment

Before annealing, TZM rods must be coated with a heat resistance layer made from anti-oxidizing material. In addition, the furnace’s pressure needs to be increased from −0.2 MPa to 0.025 MPa after its gas environment changes to inert gas from vacuum.

As the heat treatment starts, the furnace temperature slowly increases to 870–980℃. After remaining at this temperature level for 10 to 15 mins, the furnace temperature rapidly rises to 1400–1600℃ and stays for 30 mins to 1 hr. When the temperature cools to room temperature, the TZM rod goes through a subsequent round of heating at 600–800℃, lasting for 30 mins to 1 hr.

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