Metal powders

Grades, production method, chemical composition and properties

Powder grades, nominal chemical composition and properties of coatings

Photo of AP-CoCr23Ni26 particles, grain size 20-56 mkm.

AP – Atomized Powder

High Steel Powders:

AP-FeW6Mo5, AP-FeMo6V1, AP-FeMo6V1Co8, AP-FeMo6V3Co8, AP-FeMo2V3Si. AP-FeW6Mo5-b is for bead-blasting treatment, microhardness is ≥400 HV 0.05 /5 (acc. to specification); 750-1000 HV (factual).

Die Steel Powders:

AP-FeCr5W3MoV5Si2, AP-FeCr6WMoV8Si, AP-FeCr3WMoV5Si, AP-FeCr12MoV, AP-FeCr12MoV3Ti AP-FeCr18MoVCo2, AP-FeCr8W2V2Co

Chemical composition

Powder grades and properties

Powders developed for special application:

CP - conglomerated powder

Particle size 40 - 100 mkm.

*New materials: Ni-Cr-Al-Y system alloys for coatings application in aerospace industry.

Alloys of the Ni-Cr-Al-Y system are most widely used to obtain coatings on blades operating at high temperatures and thermal stresses.

Sprayed powders may be delivered with other particle size not presented in the table, in microns: 45-125, -125, 100-140, 100-280, 160-280, 280-400.

Properties of NiAl metallides

Erosion-resistant alloyed powders AP-FeCr17Ni8Si6Mn (ZN-6L) and AP-FeCr18Ni9Mo5Si5Mn4Nb (ZN-12M) were developed for high-performance and high-quality plasma-jet hard-facing of wear-resistant coatings onto sealing surfaces of power equipment valving parts in lieu of the coating electrodes well-known in the valving industry. Powder grades designation in brackets are the grades of coating electrodes according to GOST 100The basic phase in the material RP-Ni70Al30 is the metallide NiAl (β` - phase >95%), while in RP-Ni85Al15 it is the metallide Ni3Al (γ`- phase >95%), and in VKNA the metallide Ni3Al (γ`- phase). The materials' structure in a coating is marked by high resistance to recrystallization during use at high temperatures.

Particle shape

Particle size

Base fraction 20-63 microns, VKNA powder 56 microns.

The typical average size (conditional diameter) of powder particles is 30-40 microns.

Physical-mechanical properties of powders and coatings

VKNA is a heat-resistant super-alloy based on the metallide Ni3Al, phase-strengthened with admixtures of infusible metals, which is characterized by outstanding physical and mechanical properties of plasma coatings: structural thermal stability, heat-resistance and wear-resistance when used as parts in gas-turbine engines at temperatures of 1150-1200 0C.

RP-Ni70Al30 Smelting temperature 1640 0C. Exclusively high heat-resistance when heated in open air, more than three times greater resistance to corrosion than the common heat-resistant alloy CrNi77TiAlB.

RP-Ni70Al30 in plasma coatings is corrosion-resistant in the atmosphere, water and in alkalis (NaOH and KOH solutions).

Surface hardness is approximately 40 HRC; the material forms durable coatings with steel and copper and is well pressed and sintered in a vacuum.

RP-Ni85Al15 Melting point is 1400 0C; excellent heat-resistance of coatings when heated in open air to 1150 0C; the material and coatings are durable in the atmosphere, water and alkalis.

Hardness of plasma coatings is approximately 300 HB; the material forms durable coatings with steel and copper.

Use

Powders of magnetically soft nickel-based alloys doped with molybdenum are super permalloys that are characterized by extremely high magnetic permeability. Light magnetization of alloys in weak fields is marked by the near-absence of magnetic anisotropism and magnetostriction effects. Molybdenum boosts the unit-area resistance and the initial magnetic permeability of permalloys and decreases their vulnerability to mechanical deformations. By applying high-purity constituents and showing special attention to thermal processing, super permalloys achieve the highest magnetic permeability among common magnetically soft materials.

Spheres of application: PM production of magnetic elements – core rods with high magnetic permeability used to equip measurement and radiotechnical devices.

Spherical molybdenum permalloy powder, sprayed with an inert gas, and with a base grain size of -100 microns (less than 100 microns) without additional sieving or sintering is used, for example, in obtaining compositional magnetic material with dielectrical isolation. In this case, powders with added insulation and plasticiser are pressed in hard matrices at high pressure; then, the semi-finished products are sintered in a vacuum or a protective atmosphere.

Self-fluxing nickel alloys Ni-B-Si and Ni-Cr-B-Si-C.

These materials are used for deposition and sintering of coatings resistant to corrosion, friction wear and abrasive particles. The coatings resist gas corrosion up to temperatures as high as 700 - 850 °C, and are resistant to fresh-and saltwater, saline solutions, oil-containing environments, ammonia and in other aggressive environments. They are not resistant, or weakly resistant, in inorganic acid solutions. The alloys melt in a range of temperatures typical of materials with eutetics in their structure. The base structural phase of coatings made from these alloys: Y - hard nickel-based super-saturated solution, chromium carbides of the type Cr23C6 and chromium carboborides; in powders with increased hydrogen content, particles of the stronger carbide Cr7C3 are also present. The coatings' hardness and wear-resistance increases as the content of chromium, boron, silicon and carbon. Boron and silicon form low-melting eutectics with nickel, with a melting point of 950-1080 °C, and restores oxide films on the surfaces of substrata with the formation of borosilicate slags (self-fluxing) in the presence of a liquid phase, and improve the substratum's wetability with liquid metals.

The adhesion, cohesion and wear-resistance of surfaces made from alloys with the same composition under dry friction and abrasive actions increases, as a rule, with higher density (reduced porosity) of the coating. Porosity of unsintered plasma coatings made from self-fluxing alloys can reach 10-12%, and that of gas-sprayed coatings can reach 20%. Reduction of the porosity of coatings and, as a result, a 5-10 times increase in strength is acheived by sintering the coating, which is done either simultaneously with annealment with plasma welding (the PTA process) or with the layer-by-layer deposition of a coating using gas-powder welding by alternating the process of layer deposition with layer fusion. Fusing sprayed layers is also done with a gas-fired burner, a plasmotron flame, through heating in a furnace, or with high-frequency currents. Thanks to their high density (with porosity generally less than 1%), detonation coatings do not require fusion following spraying. Porosity's impact on the quality and workability of coatings is complex. In conjugated surfaces, under semi-dry friction, the optimal porosity - obtained, for example, through plasma spraying without fusion, can promote low wear in a friction assembly. The pores, by accumulating lubricants, can prevent fretting of conjugated surfaces.

Dilatometric studies of sprayed coatings made from the base alloys NiCr13Si2B1, NiCr15Si3B2, NiCr16Si3B3, NiCr17Si4B4 has shown them to be free of phase transmutations when cooling in the range of temperatures from 960 to 20°C. For this reason, phase transmutations occuring in an iron-carbon system with changes in volume can lead to the danger of surface fracturing in steel and cast-iron substrata during cooling. Therefore, it is recommended to cool products with applied coatings made from self-fluxing alloys at a slow pace. The interval of recommended cooling speeds is, for example, for steel 10 – less than 100 100 °C/s; for steel 45 – less than 35 °C/s; for steel 70 – less than 5 °C/s. The general characteristics of Ni-Cr-B-Si-C also include the tendency to maintain hardness and resistance to abrasive wear following drawing-back with heating to 600 °C. The hardness of alloys at high temperatures (“hot” hardness) - for example, at 650 °C - can reach 50-70% of that measured at room temperature.

The field of application of powders made from nickel alloys includes: wear-resistant coatings on parts for metallurgic, mining and oil-extracting, energy, glass and chemical equipment, stamping and pressing instruments, car, train and boat parts, gas-pumping devices, agricultural technology, etc. The alloys are also used to produce mixtures with other materials for use in coatings: carbides, intermetallic compounds, and others.

Self-fluxing iron-based alloys are represented by the high-carbon alloys AP-Cr4Mn2Si2B4V1, doped with vanadium, chromium and manganese, and the iron-nickel-chromium alloy AP-G14 and the medium-carbon alloys FMI with eutectic composition. Coatings made from high-carbon alloy is marked by increased hardness and high resistance to abrasive wear in an aqueous environment, while eutectic alloys (FMI) boast resistance to friction wear at high slipping speeds.

The self-fluxing lead-nickel bronze Cu-Sn-Ni-B-Si is a material for creating wear-resistant coatings for products made from copper, copper alloys, and steel.

Self-fluxing alloys are produced by gas-spraying a molten solution. The resulting polydispersed powders are subjected to screening into fractions that are narrow in terms of particle dimensions for use in various technologies for spraying and welding coatings: detonation and supersonic spraying, gas-powder coating welding, gas-fired and plasma spraying, laser and electrospark welding, and plasma and induction welding.

Particle sizes (base fractions)

Base fractions of powders for various coating technologies:

Based on the client's needs, we can produce powders with other particle sizes. The minimal dimensions of meshes used to classify powders are: - 40 microns (~400 mesh) and 45 microns (325 mesh). Powders are not screened on meshes of less than 40 microns, since gas-sprayed powders typically contain a small amount of fine particles of less than 15-22 microns.

The shape and structure of powder particles

Gas-sprayed powders are primarily spherical in particle shape, with the structure of a cast material

*Fig.1, fig.2: The shape and structure of powder particles in the nickel-based alloy AP-NiCr15Si3B2.

*Fig.3, fig.4: The shape and structure of powder particles in the iron-based alloy AP-FeCr4Mn2Si2B4V1.

Flowing temperature of coatings

Dilatometric analysis of self-fluxing alloys, heat content curves include the following characteristics points: the temperature at which the liquid phase appears, T0, and the temperature at which the maximum change in heat content is observed, Tm, (the peak of flowing on a DTA curve). This range of flowing in self-fluxing alloys, the parameter ΔT = T0 – Tm, plays an important role in selecting the optimal flowing temperature for a coating. It is recommended that the flowing temperature be as close as possible to Tm, at which the coating become more dense (porosity disappears), and a transitional diffusive layer of the necessary thickness is formed and the maximal strength of the coating and substratum is reached. In actuality, nickel alloys of the system Ni-Cr-B-Si-C that contain nickel borides and silicides, as well as chromium borides and carboborides, flow in a wider range of temperatures than ΔT, with gradual assimilation during flowing, during heating (dissolution in nickel) of clusters of high-melting compounds.

Powder characteristics and fields of application

Notes to table:

Tm – melting point (the first peak on the heat content curve of a DTA), reference data;

TS - solidus temperature;

TL - liquidus temperature;

f – friction constant in a friction pair with steel, reference data;

The characteristics of materials and coatings provided in the table are for reference only.

Sample coating structures

*Fig.5: Fused coating made from the alloy AP-FeCr4Mn2Si2B4V1 a steel substratum (etching treatment). Coating hardness 63 HRC

*Fig.6: A fragment of a cylindrical detail – a plunger of a drowned oil pump. Fused coating made from the alloy AP-NiCr17Si4B4-U (etching treatment) Coating hardness 58 HRC

Brades and chemical composition

Particle size, packed density and compressibility of powders

Zink powder AP-Zn
Chemical composition, %

Powder of Zn-Al alloys AP-ZnAl16
Chemical composition, %