Plasma rapidly quenched coatings with the special physical properties
Rapidly quenched materials are shaping by plasma spraying with speeds of cooling up to 108 K/c. These speeds are providing by separated solidification of the disk-shape fractions with thickness 1-15 µ . Separated solidification of the particles allos to provide those speeds of cooling by spraying coatings with thickness up to a few millimetres. The microcrystal or amorphous shape of the coating depends on the spraying material. The coating can be transfered from amorphous to nanocrystal shape by following heating. Rapidly quenched coatings have higher level of the physical and chemical features: corrosionproof, soft-magnet and other. In order to obtain rapidly quenched coatings with peculiar properties by spraying powders with the particles size of 20-80 µ, a new method of plasma spraying in the air with protection from the surrounding atmosphere has been developed. The method of spraying is protected by a Russia patent. The method is based on the standard equipment for a plasma spraying. The spezial nozzel to plasmotron was dewelopment by the patent. This nozzel fllows following:
- to increase heat transfer from plasma to the spraying particles;
- to eliminate thermal influence of the plasma to the shaping coating;
- to decrease content of the air oxygen in spraying flow in 4-20 time;
- to shape the metall alloys coating with amorphous structural thickness
- up to a few millimetres.
Standard industrial plasma equipment has plasmotron (fig.1, position 1)..
Fig. 1. A new method of plasma spraying with a special nozzle to a plasmotron
Spraying powder with transportable gas (position 2) is perpendicular directed into the plasma flow (position 3). The conical space inside of designed nozzel (position 4) protects the spraying particles from atmospheric oxygen and improves heat transfer from plasma to the spraying particles due to its small volume and hot (up to 1500 o C) walls of nozzle. Spezial device on the exit of the nozzle provides practically entire elimination the heat influence of plasma flow on the coating (position 5) and substrate (position 6).
On the basic of suggested method, several technologies of making objects, protected by the amorphous coating, have been developed. The technology of obtaining amorphous coatings, processing soft-magnet properties, makes our investigations completed to a large extent. Coating with thickness up to 50-1000 µn; (аnd more) shaped by plasma spraying powder standard cobalt-based alloy Co58Ni10Fe5B16 Si11. Such coatings exhibit shielding properties against electromagnetic radiation (constant and alternating field) and are designed for protect electronic circuits, sensors, gyroscopes. The following cases and blocks with shielding coatins have been made:
- commutation block, measuring 400 300 220 mm (15.75 11.81 8.66 in);
- copper case, measuring 48 13 13 mm (1,89 0,51 0,51in), with thickness of screening coating 0,15 mm (0,006 in) for protection of microcircuits;
- aluminium (berilium) case of a gyroscopes of 60 mm (2.36 in) diameter and length of 100 mm (3.94 in) (for protection of the inside parts from against constant influence of magnetic fields and magnetic fields of Earth; screening coefficient of the constant fields equal 250 mOe - 2,5 Oe provides 30 - 80 dB at thickness of coating 0,25 mm (0,01 in));
- micro-telephone receiver case, measuring 200 50 40 mm (7,87 1,97 1,57 in), covered by the 0,4 mm (0,016 in) thickness coating to protect confidentiality of the conversation;
В настоящее время аморфные материалы для экранирования применяются в виде переплетенных аморфных лент, что предполагает ручной труд. Кроме того, экраны из аморфных лент сложно закреплять на поверхности изделий. Аморфные покрытия имеют адгезию к подложке 3 кг/мм2.
Получены металлические покрытия с аморфной структурой на пластмассах, что расширяет круг объектов с экранирующими покрытиями. Так экранирование ЭВМ существенно уменьшит воздействие электромагнитного излучения на человека.
Screening coefficient for micro-telephone case and for microcircuits case depend from field frequency and are listed in the table below:
|Field Frequency, Hz
||Shielding Coefficient Micro-telephone, dB
Microcircuits Case at
Now for a screening are using like binded amorphous tapes, that require hand labor. Also, fixing of screens from amorphous tapes on the surfase of products is veri difficult. The amorphous coating have adhesion to the substrate 30 MPa.
Fig. 1. The case of a gyroscope (Al, Be) with a amorphous soft - magnetic coating of alloy Co58Ni10Fe5B16 Si11
Metal coating with an amorphous structure have been obtained on the plastic surfase. This widens the range of objects (sensitive to heat) with shielding coatings. For instance, shielding of computers screens will significantly decrease influence of electromagnetic radiation on a human.
Formation of the corrosion-, wear-resist coatings is an additional application of the suggested method .