Thin wall, small diameter TZM tube made of TZM (titanium zirconium molybdenum) alloy is critical component in a broad array of industrial applications. These include parts of electron tubes; thermocouple retainers; high-temp furnace heaters; and as rotary targets for coating common in solar industries; among many others.
While TZM is typically about more expensive than pure molybdenum, its properties are more desirable in certain applications. TZM tube is stronger, harder, more ductile, more creep resistant, and has a higher recrystallization temperature than pure “moly,” making it less likely to weaken, soften, or become brittle as temperatures increase.
The fabrication of thin wall, small diameter tubing made of TZM begins with isostatic pressing and high-temperature sintering of pure powder forms of the constituent metals. Further processing yields highly condensed TZM rods. With great skill and precision, a centerline hole is then drilled throughout the entire length of each rod. This is followed by warm and cold rolling operations.
After rolling, a tubular annealing machine heat-treats each TZM rod, which is then cooled to room temperature. Next, a lubricant-covered tungsten/molybdenum alloy rod is inserted into the previously drilled centerline hole of the TZM tube. The rod is reheated to be drawn with/without the insert multiple times until the tube’s dimensions and surface quality meet specifications.
TZM tubing produced in this way yields superior surface quality, high dimensional precision, and excellent mechanical performance, all compatible with high-volume production. Tubes as thin as 0.5mm or lower, with diameters of 10mm or lower, and lengths to 4,000mm or longer are possible. Tube roughness can range from 0.6um-1.2um. Typical mechanical properties are 802 MP tensile strength (Rm), 651 MP yield strength (Rp 0.2), and 13.5% longevity(A).
The Process in More Detail
The TZM tube manufacturing process involves four major steps: formation, heat treatment, surface treatment, and drawing.
TZM Tube Formation
TZM powders are tightly packed into a rod-shaped rubber die. Highly condensed, they are then isothermally pressed into rod form. A vacuum sintering furnace heats the pressed rod to an extremely high temperature, around 1300℃. The sintered TZM rod is straightened and drilled along the entire centerline on a specialized drilling machine. This is followed by warm (700℃-900℃) and cold rolling operations. Rolling pressure is between 110KN-190 KN.
TZM Tube Heat Treatment
After rolling, TZM tubing is placed in a special annealing furnace at 850℃-1050℃ to remove residual stress. The furnace is filled with a reducing gas such as hydrogen. Annealing time varies from 10 to 60 minutes, based on the tube’s dimension.
TZM Tube Surface Treatment
The annealed, stress-released TZM tube is evenly covered with a layer of lubricant, which may be pastes of graphite or MoS2. The lubricated tube dries at 120℃-200℃ for 30-120min while a tungsten/molybdenum alloy rod remains inserted in the centerline hole.
TZM Tube Drawing
Warm drawing of the TZM tube involves multiple, repeated operations. Specially designed drawing machines and dies produce small-diameter TZM tubes to exact specifications.
The internal shape of the dies must be cylindrical, with a diameter somewhere in between the tube’s inner diameter and the insert’s outer diameter. Drawing speed varies from 1mm/s-5mm/s on each insertion-withdrawal operation. The deformation rate is 5％-20％. Temperature in the warming area is 450℃-1000℃. The temperature of the drawing die ranges from 300℃-800℃. Each batch of TZM tube required 2 to 4 sets of different drawing dies.