Key Performance Characteristics

 
SHS 7170 coatings exhibit good combinations of corrosion and wear resistance, high impact resistance and superior bond strength. Superior bond strength values signify that this material has exceptional adhesion and cohesion. High adhesion values highlight extremely low residual stress (even at high thicknesses) inherent in this coating type. High cohesion values mean the probability of “pull-out” of individual particles during wear, erosion and other service conditions is extremely low. Low porosity means low coating permeability, resulting in a highly corrosion resistant barrier. Low oxide content is another key ingredient contributing to high bond strength due to the very limited presence of internal voids and other defects. These characteristics provide predictable coating performance across a broad variety of service environments. SHS 7170 is especially resistant to elevated temperature sulfidation attack and widely used for elevated temperature erosion/corrosion protection of heat exchange tubes in coal fired boilers.

Universal Applicability
When SHS 7170 is sprayed directly onto substrate alloys using conventional substrate preparation practices and without a bond coat, extremely high bond strength is achieved. Extremely high bond strength is achieved for SHS 7170 coatings in ASTM C633-01 adhesion and cohesion strength on plain carbon steel (12.040 psi), stainless steel (10,180 psi) and difficult substrates to bond to such as aluminum (10,800 psi) and copper (4,800 psi). SHS 7170 can be easily applied in the field with a wide processing window and very good spray “forgiveness.” Two optical micrograph images to the right of as-sprayed SHS 7170 TWAS coating structures are shown as a function of spray angle and distance from the surface. Superficial hardness (15N) and porosity from metallographic analysis are included for each micrograph. As indicated by the coating structure and coating properties, insignificant changes are occurring in the coating structure and resulting properties, verifying a very large process spray window.

Ability to Repair Worn Surfaces
Under the right conditions, SHS 7170 can be sprayed up to 1” (25 mm) thick as a cost-effective option for rebuilding worn out industrial parts and components. The coupon in the photo to the right is an example of an SHS 7170 coating sprayed to a thickness of 0.800” (800 mil or 2 cm). In the following table, the bond strength of SHS 7170 coatings on 1018 steel substrates is shown as a function of coating thickness. Extremely high bond strength is maintained up to at least 100 mil thick when using the optimal spray conditions, which also minimizes residual tensile stresses.
 

 
Elevated Temperature Erosion Resistance
Because it offers combinations of corrosion resistance and high hardness in high sulfur and elevated temperature environments where fly-ash and bed-ash erosion occurs, SHS 7170 is superior to nickel based superalloys and other TWAS coatings applied in coal fired boilers. In elevated temperature erosion measurements using bed ash from an operating CFCB boiler, SHS 7170 coatings provided increased lifetime, depending on angle of impingement, from three to eight times over 1018 wrought steel plate and 1.5 to 3.5 times over wrought 625 nickel alloy plate.

Damage Tolerance
Impact testing on SHS 7170 TWAS coatings was performed using a Gardner Impact testing machine. A 12 lb test weight with a 0.5” diameter impact punch was dropped from 40” in height onto as-sprayed and heat-treated SHS 7170 TWAS coating samples, each with a 10 mil thick coating. Prior to impact testing, the heat treated sample was thermally cycled 10 times between a 10 minute soak in a 600°C furnace and air qunched to room temperature. Both samples survived 480 in-lbs impact without chipping, cracking or delaminating, while demonstrating the ability to deform with the substrate.

Spray Parameters
For SHS 7170 TWAS spray parameters, contact NanoSteel at 1-877-293-NANO or info@nanosteelco.com.