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Molybdenum alloys MoW, MoLa and others

Some properties of molybdenum that are important for industrial use include its high melting point, high elasticity modulus, low temperature linear expansion coefficient, good plasticity at low and room temperatures, heat-resistance, high electric and heat conductivity, relatively small capture cross-section of thermal neutrons and almost half the density of tungsten.

Some drawbacks of molybdenum as a construction metal are its susceptibility to oxidation at temperatures higher than 500–700 °? and the fact that it is not sufficiently heat resistant to be used in conditions of extremely high temperatures and lengthy loads. Alloying of molybdenum has practically no effect in terms of eliminating the first drawback, but does make it possible to significantly raise the recrystallization temperature, tensile strength and creep resistance at high temperatures, and, for dispersive hardeing-for example, using lanthanium oxide-to increase heat resistance and improve plastic properties (lower the fraility threshold).

Below is the list of products made from alloyed molybdenum:

  • Hot-rolled sheet from molybdenum- tungsten alloy MoW-PM.
  • Extruded and tooled products from molybdenum- tungsten alloy MoW-2-PM.
  • Crucibles from molybdenum- tungsten alloy.
  • Products from molybdenum, tungsten and their alloys for high-temperature furnaces.
  • Products from the molybdenum- tungsten alloy MoW10-PM for sputtering targets.
  • Rolled stock and products from lanthanium-treated molybdenum MoLa-PM.
  • Stock materials made from MoWCu-PM.
  • Tooled stock materials made from MoY-PM molybdenum alloy.

1. HOT-ROLLED SHEETS FROM MoW-PM MOLYBDENUM- TUNGSTEN ALLOY

Use

The molybdenum alloy MoW, strengthened by forming a solid solution with tungsten (nominal composition by mass percentage: Mo 70%, W 30%, content of alloying component ± 2%), boasts a higher recrystallization temperature than molybdenum (as high as 1200 °? with a deformation ratio of 90%), resistance to high temperatures, resistance to corrosion and creep (creeping at high temperatures).

Rolled stock made from MoW alloy is used to make components for high-temperature furnaces, electrodes for power semiconductors and other purposes.


Dimensions of sheets made from MoW-PM alloy
Thickness, mm Width, mm Length, mm
0.8–0.9 From 30 to 300 From 80 to 1000
1.0–3.0 Up to 500 Up to 1000
3.1–15 Up to 500 Up to 1000

Sheets are delivered annealed for internal stress removal and with tested microstructure.


Guaranteed mechanical properties of sheets at room temperature

Sheet thickness,
mm

Tensile strength σ?,
N/mm2 (kgf /mm2), minimum
δ, %,
minimum

Sheet properties, transversal direction

0.8–0.9 830 (85) 8
1.0–3.0 780 (80) 8
3.1–6.0 780 (80) 6

Mechanical properties of small-scale sheets (thickness of up to 110 mm, length up to 250 mm) are set based on the client’s request.

2. EXTRUDED STOCK FROM MoW-2-PM ALLOY

Use

Products made from strengthened MoW-2-PM molybdenum-tungsten alloy are used to produce components operating in difficult, stressed environments at increased temperatures (up to 2100 °C).

Stock is produced using powder metallurgy, with technical support from specialists at the Central Science and Research Institute for Materials (OAO CSRIM) and the Powder Metallurgy Institute at the Central Science and Research Institute for Iron Metallurgy (PMI FGUP named after I. P. Bardin «CSRIIM»).

Stock dimensions

Tooled stock is produced in the following dimensions:

  • round, with diameters of Ø 36, 53;
  • rectangular, cut to 64×46, with a length of at least 350 mm.

The surface coarseness of tooled products does not exceed 6.3 microns.
At the client’s request, products with other dimensions can be produced.
Stock is delivered having undergone thermal treatment and with testing for microstructure and mechanical properties.

Guaranteed mechanical properties of MoW-2-PM extruded stock

Dimensions, shape,
mm

Thermal treatment variant *

Specimen type**

Mechanical properties (minimum) at testing temperature

20°C

150°C

1800°C

σ?, MPa δ, % σ?, MPa δ, % σ?, MPa δ, %

64×46

?

lengthwise 650 5.0 n/a n/a 50 5.0
transverse 500 1.0 500 2,0 50 5.0

?

lengthwise 500 5.0 n/a n/a 45 5.0
transverse 450 2.0 450 2,0 45 5.0

Ø 53

?

lengthwise 650 5.0 n/a n/a 50 5.0
transverse 500 0 500*** 2.0*** 50*** 5.0***

Ø 36

?

lengthwise 500 5.0 n/a n/a 45 5.0
transverse 450 0 450*** 2.0*** 45*** 5.0***

Notes:
* Thermal treatment variant
? — at 1300 ? ?
? — at 1400 ? ?
** Specimen type:
lengthwise, transverse — direction of the specimen’s cut with regard to the direction of extrusion.
*** properties not determined, guaranteed by the technology
n/a — properties not determined
With a relative elongation of δ ≥ 2%, a conditional yield limit of σ0,2 is achieved. Typical values for mechanical properties exceed the guaranteed parameters by 15–35%.


Sample actual characteristics of extruded and annealed (for internal stress removal) rods from MoW-2-PM alloy at room temperature and at 1800 °C

d, ?? *

ε , % * *

σ?, MPa δ, % σ?, MPa δ, %

20? ?

1800? ?

53 75 760 11.8 57.6 / 54.8 22.6 / 14.0
36 79 790 16.0 62.0 / 61.2 24.0 / 14.0

Note:
* rod diameter
** deformation ratio
Figures including fractions (/): the numerator indicates data obtained during testing of lengthwise specimens, and the denominator indicates data for transverse specimens.

3. MoW30-PM CRUCIBLES FROM MOLYBDENUM- TUNGSTEN ALLOY

Use

MoW30 molybdenum-tungsten alloy, strengthened with a solid solution of tungsten, features temperature resistance and creeping resistance that is higher than molybdenum, and higher machinability than tungsten.

MoW30-PM crucibles made from sintered and forged molybdenum-tungsten alloy are used primarily to melt corundum in technologies for growing extremely pure sapphire monocrystals.

Chemical composition of crucibles

Molybdenum is the base, with 28–32% tungsten. The alloy may be additionally strenghened with admixtures of B, Hf, Y, Zr, C.

Recommendations

Shape and dimensions

Crucibles are produced in accordance with drawings. The shape and dimensions are agreed upon with the client. Surface roughness of tooled crucibles does not exceed Rz 6.3.

Crucible density:

Sintered MoW30-PM crucibles — at least 10.9 g/cm3
Forged MoW30-PM crucibles — at least 11.2 g/cm3


Recommendations on crucible storage and use.
Recommendations on the use, transport and storage of crucibles can be found in the section entitled «Tungsten. Tungsten Crucibles».


4. PRODUCTS MADE FROM MOLYBDENUM, TUNGSTEN AND THEIR ALLOYS FOR USE IN HIGH-TEMPERATURE FURNACES

Use

Products made from molybdenum, tungsten V-MP, and the molybdenum alloys MoW30-PM (MoW30), MoLa-PM are used to outfit vacuum and hydrogen furnaces, the heat zones of units for smelting quartz glass and growing sapphire monocrystals, furnaces for the annealment of uranium fuel in the manufacture of fuel rods and for the production of components for high-temperature heat exchangers, thermoelectric converters and other devices that operate at high temperatures.

Shape and manner of production

Products are made in sintered form or from deformed (by forging or rolling) stock (sheets, plates, forced products, rods) according to the client’s drawings or according to a manner of production, geometric dimensions and tolerances for dimensions and surface roughness submitted by the client.
Products are made in simple shapes: tooled discs, slabs, rings, plates, substrata, bearing plates, rods, or electrodes; or in complex shapes: thermal screens, radiators, boats, fastening details, etc. Additional requirements regarding product specifications are set based on the client’s request.

Recommendations on use

Before use, thermal screens and other products used in a customer’s vacuum furnaces should be annealed in a vacuum of ?<10–4 mmhg (torus) in the following manner:

  • heat to 1000 °? for over a period of at least 3 hours,
  • hold at approximately 1000 °? for at least 1 hour,
  • heat to 1400–1500 °? over a period of at least 1 hour,
  • hold at approximately 1400–1500 °? for at least 1 hour,
  • heat to 2000–2200 °? over a period of at least 1 hour,
  • hold at approximately 2000–2200 °? for at least 1 hour,
  • cool the products in the furnace.

During use, the products should not be subjected to shocks.

5. PRODUCTS FROM MOLYBDENUM- TUNGSTEN ALLOY MoW10-PM FOR SPUTTERING TARGETS

Use

Products made from MoW30-PM (MoW10) molybdenum-tungsten alloy are used as sputtering targets in technologies of thin films to produce electronic components and other functional coatings, as well as to produce components for high-temperature vacuum and hydrogen furnaces.


Guaranteed chemical composition of MoW10-PM 99.95% products
Element Mass percentage
Mo+W 99.95% minimum
W (10.0 ± 1.0) %

Impurities, ppm, maximum

Fe 100
Al 50
Ni 50
Si 100
Total metallic impurities 500
C 100
O 70
N 50

Other requirements for the products' chemical composition may be agreed upon based on the client’s requests.

Product shape and dimensions

Products are made in the form of tooled plates, discs, rings, cylinders (rods) and in simple and complex shapes.
The shape and dimensions of products and surface characteristics are determined based on drawings agreed upon with the client.

6. ROLLED STOCK AND PRODUCTS MADE FROM MoLa-PM LANTHANUM-TREATED MOLYBDENUM

Use

In the late 1990’s, a molybdenum alloy dispersion-strengthened with lanthanum oxide-so-called ODS-Mo-won widespread recognition and use abroad. POLEMA produces an alloy of this kind, under the brand MoLa-PM (lanthanum-treated molybdenum).

ODS-Mo is recommended as a more stable material for replacing other molybdenum alloys in a number of spheres for use in high (1600–1800 °? and higher) temperatures:

  • electric engineering: radiators, thermal screens, circuit breaker parts and incandescent lamp parts;
  • atomic energy and power systems: creep-resistant boats for smelting nuclear fuel, high-temperature springs, high-temperature convertors, vanes and tracks for cyclical turbines;
  • atomic energy and power sysyems: creep-resistant boats for smelting nuclear fuel, high-temperature springs,high-temperature convertors, vanes and tracks for cyclical turbines;
  • the space and rocket industry: parts for jet apparatuses, high speed engines, and rocket combustion chambers;
    and other industries.

Lanthanum oxide, introduced into the system and enveloping molybdenum grains, serves as a displacement barrier to dislocations during the deformation process, which allows the alloy structure to stabilize; with small grain sizes, it ensures tensile strength and resistance to creep at high temperatures. Other well-known industrial alloys-for example, stabilized with carbides of titanium and zirconium-of the type ??-TZM (Mo-0,5Ti-0,08Zr, 0,01–0,04 °C mass %) ? Mo-TZC (Mo-1,2Ti-0,3Zr, 0,25 °C mass%), are less stable, since at high temperatures the carbide constituent becomes coarse or dissolves within the molybdenum matrix.

Molybdenum alloy that has been dispersion-reinforced with lanthanum oxide has the following advantages over molybdenum: a significantly lower cold shearing threshold following annealment (with internal stress removal), higher tensile strength at room temperature, high plasticity in a recrystallized state, more than 1.6 times greater tensile strength  at 1600°C and significantly higher (an order of magnitude greater) resistance to deformation during tests for long-term tensile strength  at 1800 °? when compared with unalloyed molybdenum obtained through arc melting or the PM method.


Guaranteed chemical composition of rolled stock and products made from lanthanum-treated MoLa-PM brand molybdenum
Element Mass percentage
Mo  
La 0,40 ± 0,07%

Impurities, ppm, maximum

Fe 100
Al 30
Ni 50
Si 50
Mg 20
Na 30
K 80
Ca 40
W 130
Total metallic impurities 500
C 100

Product shape and dimensions

Products made from MoLa-PM are produced in the form of rolled sheets, slabs, plates, discs, forged rods, boats, screens, and radiator components.
Sheet it produced with thickness of 0.5 mm or greater.

Below are the guaranteed tolerances for dimensions and surface quality of rolled stock:
thickness ± 0.10%;
width ± 0.8 mm;
length ± 1,6 mm per 304,8 mm of length;
roughness of a milled or ground surfaces shall not exceed 40 Rz.

Concrete dimensions and tolerances for thickness, width and length of rolled stock, forged stock or tooled products, including requirements for surface roughness, are set in accordance with client requests. Unless otherwise specified, the roughness of a milled or ground surface does not exceed Rz40.
Products with complex shapes are produced based on plans.


Mechanical properties of MoLa-PM rolled stock

Width, mm

Tensile strength σ?, N/mm2 (kgf/ mm2) Relative elongation
δ, %

Minimum

From 1.0 to 2.0 mm inclusive 690 (70) 5
> 2.0 to 4.0 mm inclusive 690 (70) 10
> 4.0 to 6.0 mm inclusive 640 (65) 8

Sheets with a thickness of less than 1 mm undergo bend testing with a bending angle of at least 90°.


Sample actual characteristics of MoLa-PM rolled sheet and forged rods
Material Test temperature, °C Tensile strength
σ?, kgf/ mm2
Relative elongation δ, %
Sheet Mo-La-PM
2.0–3.0
20 88–98 10–12
Rod Mo-La-PM
Ø 9.5
20 74–75 30–35

Rod Mo-La-PM
Ø 20

1400 8.2–9.0 31–39
1800 6.3 9.2

Mo-La-PM material dispersion-strengthened with lanthanum oxide shows excellent resistance to creeping. Its operational life in the form of screens and radiators in resistance furnaces is more than twice the useful life of components made of pure molybdenum. The material maintains its fibrous structure throughout extended operation at high temperatures. Moreover, radiator and screen components made of 0.4–0.5 mm maintain plasticity at room temperature in a recrystallized state.


Fig.2:
Microstructure of MoLa-PM sheet with a thickness of 1 mm
Distribution of lanthanum in the structure of dispersion-strengthened molybdenum MoLa-PM

7. STOCK MADE FROM MoWCu-2-PM MATERIAL

Stock is produced using powder metallurgy with technological support from specialists at the Institute of Powder Metallurgy at the Central Science and Research Institute for Iron Metallurgy (IPM FGUP «CSRIIM» named after I. P. Bardin).

Use

Compositional material based on molybdenum-tungsten alloy infiltrated with copper shows tensile strength at high temperatures and resistance to gas erosion. It is used to make parts for new equipment operating at high temperatures and with dynamic loads.

Material characteristics

Currently, MoWCu-2-PM material is used to produce tooled stock in cylindrical form with a diameter of 50 or 70 mm. At the client’s request, products of other shapes and dimensions can be produced.

The stock’s density following infiltration of the sintered frame is at least 11.0 g/ cm³.

8. STOCK MADE FROM MoY-PMMOLYBDENUM ALLOY

Stock is produced using powder metallurgy with technological support from specialists at the Institute of Powder Metallurgy at the Central Science and Research Institute for Iron Metallurgy (IPM FGUP «CSRIIM» named after I. P. Bardin).

Use

Dispersion-strengthened deformed MoY-PM molybdenum alloy is intended for use in preparing parts capable of working for extended periods at high temperatures.

Material characteristics

Currently, tooled stock made from MoY-PM alloy is produced in the form of rods with a diameter of 66 mm and a length of no less than 310 mm, and with a diameter of 90 mm and a length of no less than 230 mm. Surface roughness does not exceed 6.3 microns. At the client’s request, products of other dimensions can be made according to drawings.

Product microstructure is monitored using an optical microscope, while the absence of internal flaws is checked for using ultrasound.

Guaranteed product mechanical features

Material

Minimal mechanical properties of semifinished products in end-fire direction based on temperature, °C

20

1800

σ?, N/mm2 (kgf/ mm2) δ, % σ?, N/mm2 (kgf/ mm2) δ, %
MoY-PM 500 (51) 8.0 27.0 (2.75) 20