Surface Modification Via Injection of High
Temperature Solid Lubricant and Wear Resistant
Particles During Laser
Laser--cladding
Dr. Douglas E. Wolfe
814-865-0316
dew125@psu.edu
C
Composite
it Coating
C ti
Objectives
Obj ti
Laser Injection
Reinforcement materials require a multitude of properties, including
resistance to corrosion, wear, oxidation, and extreme temperatures, as
well as the ability to provide lubrication. Using the laser-clad process,
composite coatings that combine materials exhibiting these properties
can be formed. In this method, matrix materials high nitrogen stainless steel and Inconel 625 are reinforced with various metallic carbide
and solid lubricant injection particles.
Process:
• 304 stainless steel
substrate is
mounted on a watercooled copper block.
• Inconel 625 and
high nitrogenated
304L powders are
fed through the
powder feeder
assembly.
• 3kW YAG laser is
directed toward
powder covered
substrate to create a
melt pool.
Matrix Materials
Metallic Carbides
ƒ High nitrogen stainless steel
and nickel-based alloy Inconel
625 (IN625)
• Powder mixture is
injected into the melt
pool with an argon
carrier gas.
• Cr3C2, WC, and WS2
powders are injected
into the melt pool
without being
exposed to the laser
beam.
ƒ MoS2, WS2, and Ag
ƒ Excellent strength and toughness
ƒ High temperature thermal
stability
ƒ High temperature solid
lubricant
ƒ Corrosion Resistance
ƒ High hardness
ƒ Low friction coefficient
ƒ Oxidation Resistance
ƒ Wear resistance
Composition
Fe
Cr
HNSS
Bal
19.3
IN625
2.5
21.5
Ni
Mn
Mo
V
5.2
5.2
2.9
Bal
0.25
9
SEM of Inconel 625 cladding (2000 µm thick) showing embedded chromium carbide powders. The majority of Cr3C2
particles are uniformly distributed within the first 450 µm
from the surface with a 25-35% volume fraction. Because
Cr3C2 has a lower density relative to IN625, most particles
remain near the top of the melt-pool during injection.
Injection of Chromium Carbide
and Tungsten Disulfide
Injection of Tungsten Carbide
SEM of Inconel 625 cladding showing embedded
tungsten carbide particles. WC particles are uniformly
distributed within the clad matrix with a 10% volume
fraction. In contrast to the Cr3C2 particles, the WC was
distributed throughout the entire clad/melt-pool region.
This is due to its higher density relative to Cr3C2.
Formation of Second Phase
Materials
C
N
0.03
0.86
0.024
0.69- 2.63
-
0.25
0.05
-
Plot showing the
Vicker’s Hardness
N mber across the
Number
laser-clad and
substrate region.
Hardness for the
HNSS clad region
(350 VHN.0500) was
significantly higher
than the hardness of
the substrate (200
VHN.0500).
Following the laser-clad composite coating of the matrix materials, and their incorporated wear resistant and lubricating particles onto a stainless steel substrate, the
micro-structure of Inconel 625 (IN625) and high nitrogen stainless steel (HNSS) clad
regions were analyzed with scanning electron microscopy, Vicker’s hardness, and
energy dispersive microscopy.
Inconel 625
Si
Vicker’s Hardness
Microstructure Data and Analysis
Injection of Chromium Carbide
Solid Lubricants
ƒ Cr3C2, TiC, and WC
High Nitrogen Stainless Steel
Etched cross-section of the high nitrogen stainless steel
(HNSS) laser clad region on the 304 stainless steel
substrate with no particle injection into the melt pool.
Microstructure in the clad region is fine grained and
appears to be free of porosity, segregation, and microcracks. Solidification initiated from the clad/substrate
interface, continuing towards the top surface of the clad.
Partial dissolution of the substrate surface was also
observed, which increases metallurgic bonding between
the substrate and the laser clad material. Hardness
measurements are shown in the figure above.
Conclusions
ƒ Wear resistant particles such as chromium carbide and tungsten carbide
were successfully injected into the melt-pool region during laser-cladding
resulting in increased hardness.
ƒ High temperature solid lubricant tungsten disulfide was successfully
injected into the melt-pool region during laser-cladding resulting in a lower
friction coefficient.
ƒ Dissolution of carbide particles was observed resulting in ternary and
quaternary metastable phases.
ƒ The distance particles were injected into the clad material varied as a
function of density. Heavier particles settled deeper into the clad region.
SEM of Inconel 625 cladding showing embedded chromium carbide (wear resistant) and tungsten disulfide (solid
lubricant). The presence of WS2 was also confirmed by
the observation of tungsten and sulfur in energy dispersive micrographs.
SEM of Inconel 625 with injected Cr3C2 particles.
Dissolution of the carbide phase was observed due to
melting resulting in metastable phases during the nonequilibrium laser-clad process.
ƒ Hardness increased significantly from the stainless steel substrate to the
HNSS clad.
ƒ Surface modification via particle injection during laser cladding increased
hardness and lowered the friction coefficient due to the incorporation of
wear resistant and solid lubricant particles.