Metallization

Metallization 

the coating of the surface of an article with metals and alloys to impart to it physicochemical and mechanical properties that differ from those of the initial material. Metallization is used to protect articles from corrosion, wear, and erosion, as well as for decorative and other purposes.

According to the principle of interaction between the metal coating and the surface being metallized (the substrate), a distinction is made among types of metallization in which the coating is bonded to the substrate mechanically, by forces of adhesion (see Table 1, Group 1); by forces of metallic bonding (Group 2); with the formation of a diffusion zone at the boundary between the adjoining surfaces, outside of which the coating consists of the applied layer of metal or alloy (Subgroup 2a); and with the formation of a diffusion zone throughout the entire coating layer (Subgroup 2b).

The technology of metallization of types 1 and 2a involves the application of a layer of material to the surface of the article, which may be cold or heated to a relatively moderate temperature. These varieties of metallization include galvanic, chemical, and flame-spraying coating processes; application of coatings by cladding, deposition of chemical compounds from the vapor phase, and electrophoresis; vacuum metallization; explosive metallization, through the action of laser beams and plasma, and by immersion in molten metals. These metallization processes are accompanied by changes in the geometry and dimensions of the item that correspond to the thickness of the applied layer of metal or alloy. Coating technology of type 2b involves diffusion saturation with metals of the surfaces of items that have been heated to high temperatures, with the resulting formation of an alloy in the diffusion zone of the element. In this case the geometry and dimensions of the part being metallized remain virtually unchanged.

Type 1 metallization of articles is done for decorative purposes, to increase hardness and wear resistance, and for corrosion protection. Because of the weak bonding between the coating and substrate, this type of metallization is not suitable for parts to be used under heavy loads and at high temperatures. Type 2 metallization of parts produces great hardness and resistance to wear, corrosion, erosion, and heat and provides the desired thermophysical and electrical properties. Type 2b metallization is used for parts subjected to appreciable static, dynamic, or alternating mechanical stresses at low and high temperatures. With a few exceptions, these types of metallization are used for the application of protective coatings to substrates of

Table 1. Methods of metallization

GROUP 1

Galvanic coatings: Cr, Zn, Ni, Cd, Cu, Pb, Sn, Ag; Ni-Sn, Ni-Co, Cr-Ni; bronze

Spraying by electric-arc or flame methods: Al, Cu, Sn, Pb, Zn, Cr, Ag, Au; bronze, brass, steel

Chemical metallization: Ag, Cu, Ni, Co, Hg, Sb, Au, Pt, Sn, Zn, PbS

Vacuum metallization on cold substrate: Zn, Cd, Al, Ti, Cr, Au, Ag, Pt, Cu, Sn, W, Mo, Ta; Zn-AI, Pb-Zn, Pb-Cd

Cathode sputtering: Au, Ag, Pt, Ta

GROUP 2
Subgroup 2a	Subgroup 2b
Cladding, including explosive metallization: Cu, Al, Ni, Ag, W, Ta, brass, bronze, stainless steel	Diffusion metallization with: Sn, Al, Cr, Ag, Au, W, Mo, Nb, Zn, Ni, Mn, Be, Ti, Zr, Ta, U
Plasma spraying: W, Mo, Ni, Al, Cr; Al2O3, ZrO2, HfO2, MoSi2, WC, NbC, ZrB2, TiB2, CrBe2
Immersion in molten metals: Zn, Sn, Pb, Al
Electrophoresis: W, Mo, Al, Cu, Cr
Vacuum metallization on heated substrate: Cr, Ti, Al, Al2O3, ZrO2
Galvanic coatings with subsequent annealing: Cr, Zn, Cd, Al, Ni, Ag	Diffusion metallization with alloys: Cr-AI, Al-Cr-Si, Ti-Cr-Si, Ta-AI
Deposition of pure metals from carbonyl compounds in the gaseous phase: Cr, Co, W, Ni, Mo, Ta
Deposition of carbides, nitrides, borides, and silicides from the gaseous phase: TiC, NbC, W2C, HfC, Cr3C2, VC, ZrC, ZrN, TaN, MoSi2, CrSi2, TaB2, Ni2B

various metals, alloys, and nonmetallic materials (plastics, glass, ceramics, paper, fabrics, and so on). Metallization is used in electrical engineering, radio electronics, optics, rocket technology, automobile industry, shipbuilding, and the aircraft industry.

The main industrial processes used for metallization with various metals are shown in Table 1.

REFERENCES

Vysokotemperaturnye neorganicheskie pokrytiia. Moscow, 1968. [Translated from English.]
Rotrekl, B., Z. Ditrych, and Y. Tamchyna. Nanesenie metallicheskikh pokrytii na plastmassy. Leningrad, 1968. (Translated from Czech.)
Roikh, I. L., and L. N. Koltunova. Zashchitnye vakuumnye pokrytiia na stali. Moscow, 1971.
Katts, N. V. Metallizatsiia tkanei, 2nd ed. Moscow, 1972.

G. N. DUBININ