This document discusses nickel-based hard coatings for wear, oxidation, and corrosion protection. It provides information on powder production methods, including water or gas atomization, fused or sintered and crushed powders, agglomerated and sintered powders, clad powders, and blend powders. It also discusses various powder materials like pure metals, alloys, superalloys, and carbides, providing examples of each along with SEM images of their powder cross-sections. The coatings are intended to improve surface properties and provide protection in industrial applications.

1. Powder’s Morphology and
Cross-sectional SEM Images for
Nickel based hard coatings
for
Wear, Oxidation and Corrosion protection
Venkataraman Bandaru
M.Tech.
Andhra University College of Engineering (A)

2. A relatively thin layer of material which is applied to cover a substrate to improve the
surface properties of a substrate.
Coatings are used to improve the surface properties like adhesion, corrosion resistance
and wear resistance.
Coating acts as a protective layer in the different infrastructure like pipelines, mining
equipments, tunnels where durability is the major importance as well as in many
industries like automotive, aerospace, oil and gas, mining, shipbuilding etc.
Coating
Hard Coating
Hard materials are used for coating to improve the surface properties like wear,
oxidation, sliding, corrosion resistance etc.

3. Industrial Perspective
The wear of the metal parts is an important failure form of materials, especially under the vile
condition are often subjected to the damage by flowing at high speed and corrosive particles
or gases.
1. Power/Energy
1.1 Boilers - Heat-transfer pipes, turbines and other structural materials in coal-fired boilers
prone to erosion coal ash particles at high temperatures.
1.2 Fluidized bed combustor’s components are subject to high frequency erosive impact
by large coal, SiO2 and bed ash particles at high temperatures and speeds causing erosion.
1.3 Land based power generation turbines under cyclic conditions is crucial in land-based
power generators in industries, erosion is induced by low concentrations of iron oxide
particles.
1.4 Hydro-electric power station, feed water pumps, high-speed hydrofoils turbines and
components of many under water parts are prone to Cavitations Erosion (CE) is caused by
the sudden change of the local pressure in the liquid. Silt Erosion (SE) is the mechanical
degradation of a surface due to the dynamic action of silt flowing along with water.

4. 2. Aerospace/Aircraft
2.1 Mobility turbines (jet engines, helicopters and hovercraft) are prone to erosion by
runway debris and sand, as well as salt and pyrolytic carbon shed from components
within the engine after extended high temperature operation.
2.2 Landing gear Nickel alloy components are usually subjected to high thermal and
mechanical stresses during flight and may result in wear and damages which deemed
them unserviceable. Due to its location, it is regularly subjected to moisture and dirt which
work themselves into the joints when the landing gear is engaged, causing it to corrode.
3. Petrochemical industry
An aggressive environment with the presence of hydrogen sulphide, carbon dioxide and
sand, which contribute to corrosion, erosion and wear of the surface. The mutual function
of corrosion and wear usually lead to their early failure. Mass loss occurs primarily
through removal of the substrate, with the oxide layer influencing the mechanism and
efficiency of degradation.
4. Mining
Mine dewatering equipment and other components such as dewatering pumps, pump
internals, valves, impellers, pump casings, pipes etc. used in the local deep mining
operations are usually subject to corrosion accelerated wear. This is caused by the
aggressive nature of the environment and sand particles in the fluid, which may be
entrapped within such systems, thereby making them very susceptible to erosion and
wear damages.

5. Powder Production Methods
1. Water or Gas Atomized powders
Metal and alloy powders are mostly manufactured using the atomization route.
Metals melting over 2000 ºK are difficult to atomize.
The main advantage of atomization is the ability to control the size distribution and the
shape of the particles rather well, within very tight limit.
Particle of water or gas atomized powders show a relatively low surface roughness.
Water atomized powders show a more irregular geometry, while gas atomized particles are
nearly perfectly spherical, but industry favours this process due to its high production rates.
The spherical shape greatly supports the flowing behavior.
The powders produced via gas atomization are relatively cleaner and have low oxide
contents.

6. 2. Fused or Sintered & Crushed Powders
Produced by crushing of a cast or sintered block and subsequent milling to achieve a
desired particle size regime. The sintered block is crushed and milled.
Crushed powder particles show a rough, fissured surface and irregular shape which leads
to rather poor flow characteristics.
Mainly used for brittle materials like oxide-ceramics or carbides.
The particles are characterized by a comparatively high density and a moderate melting
behavior.
3. Agglomerated & Sintered powders
Due to a large surface/volume ratio agglomerated & sintered powders show excellent
melting behavior and flowing characteristics are relatively good due to nearly spherical
shape of most particles. Composite strength can be improved by annealing.
The process is well established for manufacturing of cermets powders, but oxide powders
are also produced.

7. 4. Clad powders
To protect surface material constituents of compound powders against direct contact with the
heat source of a thermal spray process or to take influence on chemical reactions.
Relatively coarse core particles are clad by fine powder particles of another constituent by
use of an organic binder. Composite strength can be improved by annealing.
5. Blend powders
Using a powder mixture is a much simpler and a cheaper approach to deposit composite
coatings.
Since the composition of individual powder particles is generally retained in the deposit
without compositional change, the coatings can be manufactured by powder composition
design.
Carbide materials are blends of chromium are an example.

8. 1. Pure Metals
1.1 Nickel
Ni – Acts to improve corrosion resistance
Coating materials
Praxair Ni-101, Water Atomized Amperit Ni-175, Water Atomized Sandvik Ni, Gas Atomized
Powder cross section
Powder cross sectionPowder cross section

9. 2. Alloys
2.1 Ni-Cr
Ni – Acts to improve corrosion resistance and Cr for oxidation and corrosion resistance
Amperit 251, Gas Atomized Powder cross section

10. 2. Alloys
2.2 NiCrAlY
Ni – Acts to improve corrosion resistance.
Cr & Al through the formation of an oxide scale. Al2O3 as an oxygen diffusion barrier that
helps to minimize bond coat oxidation and Cr2O3 to combat hot corrosion and sulfidation.
Y - Acts to improve the adhesion of oxide layer in the coats.
Amperit 413, Gas Atomized Praxair Ni 246-3, Gas Atomized
Powder cross sectionPowder cross section

11. 3. Super-alloys
3.1 Ni-Base Super alloy Ni-19Cr-18Fe-3Mo-0.5Al-5.1(Nb+Ta)-0.95Ti-0.05C (Similar to
Inconel 718). They are not able to meet the requirements of both the high-temperature
strength and the high-temperature erosion–corrosion resistance simultaneously.
Metco Diamalloy 1006, Gas Atomized Powder cross section

12. 4. Carbides
4.1. WC-Ni
The nickel serves as a matrix that improves overall coating integrity and corrosion
resistance, while the tungsten carbide constituent serves as a hard phase that assures wear
resistance.
Amperit 547.074, Agglomerated & Sintered Amperit 544.059, Dense Coated (Clad)
Powder cross section

13. 4. Carbides
4.2 Cr3C2-25NiCr
The nickel-chromium alloy serves as a matrix that improves overall coating integrity and
corrosion resistance, while the chromium carbide constituent serves as a hard phase that
assures wear resistance.
Praxair CRC 106, Blended Praxair CRC 300-1, Fused& Sintered Amperit 593, Sintered & Crushed
Powder cross sectionPowder cross sectionPowder cross section

14. 4. Carbides
4.2 Cr3C2-25NiCr
The nickel-chromium alloy serves as a matrix that improves overall coating integrity and
corrosion resistance, while the chromium carbide constituent serves as a hard phase that
assures wear resistance.
Metco Diamalloy 3007, Chemically Clad Metco Diamalloy 3003 NS,
Powder cross sectionPowder cross section