Introduction
The Nano-Core® Alloy Technology is a significant advancement over the traditional cored wire technology with the use of nano-scaled particles agglomerated with metallic matrix powders. The nano-scaled particles can be of various types of ceramics such as WC or CrC and the size and distribution dictate the final coating morphology, density and ultimately performance. The current offering of Nano-Core materials are segregated into four categories; WearX®, AshX®, CorrodeX® and CustomX®. Whereas the WearX® is an iron-based material, AshX® is tungsten-nickel based, CorrodeX® is nickel-chromium based and CustomX® can be just about any combination thereof. Nano-Core® Alloy Technology is offered primarily as a 1/16” diameter wire for the low cost twin wire thermal spray, but this wire can be welded or sprayed via single wire arc spray, combustion arc spray and PTWA. The twin wire thermal spray is the primary method for applying the Nano-Core® Alloy Technology and is capable of minimal oxide stringers due to the synthesis that occurs during the spraying process. A preferential oxidation of the smaller particles generates a partial reducing shroud thus minimizing the oxidation of the important metal compounds. Now the thermal spray coating is predominately metallic in nature, low in oxides and consists of blends of elements not available in wrought, cast or forged alloys. The twin wire arc spray method is much lower in cost to operate than HVOF or plasma spray processes, and, coupled with the material flexibility of the Nano-Core® Alloy Technology, the combination results in excellent coatings never thought possible before.

The fundamental Nano-Core® Alloy Technology is based on the ability of the ceramic nano-sized particles to preferentially oxidize during the spray process thus creating a reducing environment from the CO(1,2) formed as a by-product. The resulting thermal spray coating has excellent bonding, low porosity and a high potential for rapid passivation based on a strong protective oxide layer produced during the application. A bond coat is usually used to further support and strengthen the adhesion to the base material. The low oxide content of the Nano-Core® technology and absence of oxide stringers are the reasons for superior adhesion and increased ductility over normal twin wire arc spray coatings. Now the Nano-Core® Alloy Technology can compete with HVOF and air plasma due to lower cost operation and the ability to apply thicker coatings.

Porosity of less than 5% is typical, and often levels are less than 3% with no interconnected sites when sprayed with the twin wire arc method. A good example of the quality and performance can be seen with AshX when put in the ASTM G48 ferric chloride test for 65 hours at 85°C. An additional test run for 70 hours at 100°C (green death) and AshX® outperformed all other alloys by three and five to one.

CorrodeX® was tested in a white liqueur test at 385°F for five days and compared to traditional alloy 625 and other proprietary alloys. CorrodeX® had no corrosion loss, minimal weight gain versus significant loss and penetration of the hot sulfur compounds enhanced by chlorides experienced by the other alloys.

Applications
The primary applications that are being targeted for the various Nano-Core® materials range from the oxidizing to sulfidation, to chloride attack as well as abrasive wear and erosion environments. In general, we have put together an offering to attack each of the major corrosion mechanisms, erosion, wear and abrasion

AshX® is capable of withstanding extreme oxidation attack while tolerating thermal shock via excellent bond strength and minor differential expansion coefficients. AshX® is also capable of resisting aerated chloride attack as noted in the ASTM G48 ferric chloride above. The high tungsten material has sufficient nickel and chromium in the matrix that forms a stable oxide layer that gives it the ideal hot toughness without the problems of unstable or typical volatility seen with standard wrought materials. The PREN number (pitting resistance equivalency number) determines the pitting potential for a material and the CPT (critical pitting temperature) is used to rank the material by testing in the ASTM G48 test.

CorrodeX® was designed for sufidation resistance as demonstrated in the white liqueur test. The key to good performance is the presence of at least 20% chromium to handle the tendency of sulfide attack. It is well known that sulfidation attack is accentuated by the presence of chlorides and excess oxygen. CorrodeX® has a nominal chromium content of about 40% to 45%, which is sufficient to handle to sulfidation and potential carburization. This is why this family of materials has done so well in the pulp and paper digester and recovery boiler environments.

Carburization occurs at elevated temperatures (750°F – 2000°F+) and it is well known that the solubility of carbon in chromium is near zero when there is at least 40% chromium in the matrix material. Most carburization is accelerated when there are other corrosives that keep the protective oxide layer unstable. Again, the high chromium levels attainable with the Nano-Core® Alloy Technology and the flexibility to add supporting elements such as molybdenum, niobium, tungsten, titanium or even aluminum allows CorrodeX® to address certain difficult corrosive environments.

WearX® is an iron based Nano-Core® Alloy Technology that is focused on slip wear, erosion and abrasion applications. WearX® can be used on almost all substrates and up to about 550°C (1022°F). WearX® develops a matrix with hardness values in excess of 750 on the Vickers scale with some of the hardest around 900. The hard matrix is homogeneous and is very stable to fairly high temperatures such that it lends itself to erosion, abrasion and slip wear applications. There are currently three offering of WearX® and several in development.

CustomX® is just as it sounds, it is a custom made alloy utilizing the Nano-Core® Alloy Technology to produce desired results for either a customer specific request or for a given application. We are working with several special applications that are expected to perform in environments that are challenging for even the most sophisticated and exotic alloys. The technology is flexible as demonstrated by the ability to address the needs by selecting any available sheath material, matrix components, a wide range of nano-sized particles and infinite combinations of sizes and distribution. Special alloys are under development that can be fused after spraying to add another dimension to the capabilities.


Summary
The Nano-Core® Alloy Technology is by far one of the most significant break-through in thermal spray and welding materials. Every new alloy developed thus far has exceeded even our own expectations. The technology is taking advantage of the very thing that has caused twin wire arc thermal spray to loose ground to HVOF and plasma methods of application. Nano-Core® technology when coupled with twin wire arc spray has already hit new heights in material development with the advent of powder chemistry flexibility as noted by producing relatively ductile coatings containing up to 50% tungsten. Contact us at World Wide Alloys to assist you with your applications.