Coating Technologies

• Cr3C2 – Based Wear-Resistant Coatings

The purpose of this study was to explore the potential of the cold spray process in applying Cr3C2-based coatings for wear resistant applications.  Improvements in properties and microstructure was achieved through nozzle design, powder characteristics, standoff distance, powder feed rate, and traverse speed.  Cold spray process optimization resulted in increased hardness and improved wear characteristics with lower friction coefficients.  Selective coatings were evaluated using x-ray diffraction for phase analysis, optical microscopy (OM), and scanning election microscopy (SEM) for microstructural evaluation, and ball-on-disk tribology experiments for friction coefficient and wear determination.  The results strongly suggest that cold spray is a versatile coating technique capable of tailoring the hardness of Cr3C2-based wear-resistant coatings on temperature sensitive substrates. Please review the following PDF:
Investigation and Characterization of Cr3C2-Based Wear-Resistant Coatings Applied by the Cold Spray Process

Metals & Ceramics Processing

Expeditionary Airfield Matting
The Marine Corp and other services routinely use AM2 aluminum 6061 matting as temporary landing, take-off, and parking surfaces.  These mattings were designed for use several decades ago, and since then, military aircrafts have become significantly heavier and now have the ability to land or take-off vertically.  The additional physical and thermal loads imposed on the matting are of concern.  The Metals and Ceramics Department conducted analysis on the matting to determine the effect of current physical and thermal loads on the material.  Mechanical testing and microstructure analysis were performed on both the base metal and welded regions before and after thermal loading that simulated actual service conditions.  Results obtained from these analyses were used in a comprehensive model developed by ARL to predict the effects of various loading conditions on matting behavior.
                                
Development of Hot-Pressed Copper Composites for Thermal Management Applications
Numerous leaps in the electronic materials industry have occurred in recent years.  With the advent of more powerful, state-of-the-art devices comes a significant increase in the thermal output of these devices.  Improved thermal packaging techniques are thus necessary to dissipate the heat expended by these higher-powered devices.  The Metals and Ceramics Department at ARL is conducting studies to develop hot-pressed copper-diamond composites to act as heat spreaders to these devices.  Cu-diamond and other composites of varying composition are being produced via hot pressing and are being tested for thermal conductivity, coefficient of thermal expansion, and microstructural analysis.  Optimum hot-pressing variables including time, temperature, and pressure are being investigated to fabricate the material.  Additional processing optimization is ongoing.  Department researchers are continually interacting with the powder manufacturer to develop and test new powder compositions and fabrication methods.  Additionally, collaborations with the Penn State Electro Optics Center and the Army Research Lab allow for implantation of the technology.

Spray-Metal-Formed High-Strength Aluminum for Ballistic Armor
Developing high-strength aluminum alloys for ballistic armor applications is desirable due to the light weight of aluminum.  Traditionally, it is difficult to produce high-strength aluminum alloys (> 90 ksi) with good ballistic properties and corrosion resistance.  The Materials Processing Division at ARL, in conjunction with industry and the Army, developed a spray metal formed (SMF) aluminum alloy with a composition, structure, and properties suitable for ballistic armor.  The materials engineers at ARL worked closely with various industry partners to develop proper extrusion, rolling, and heat treating practices suitable for the SMF alloy.  After final processing, plates underwent several series of ballistics testing at the Army Research Lab.  The ongoing collaborations with industry and the Army Research Lab allowed researchers at PSU-ARL to develop an improved high-strength aluminum alloy for ballistic performance.

Corrosion Engineering

• Protection of Magnesium Alloys with Corrosion Resistant Aluminum Coatings

Magnesium alloys are frequently used in the fabrication of aircraft components due to their good mechanical properties and low density.  Due to poor corrosion resistance, magnesium alloys require multi-layer hazardous coating systems and frequent repair or replacement.  A low-cost environmentally friendly solution is the application of an aluminum barrier coating to the magnesium by the Cold Spray process.

In the present study, Cold Spray coatings of aluminum alloys (commercially pure Al (99.5%), high purity Al (99.95%), Al-5356, and Al-4047) were applied to ZE41A-T5 magnesium.  The coatings were evaluated for corrosion resistance by electrochemical testing to determine pitting potential, ASTM B117 Salt Spray, and ASTM G71 Galvanic corrosion.  Coating adhesion was evaluated by ASTM C633.  The coatings were demonstrated as effective corrosion barriers to salt water corrosion.  HP Al coatings provided the best galvanic compatibility with Mg, showing essentially no galvanic effect.  Coatings of CP Al, Al-5356l and Al-4047 resulted in galvanic currents almost 50 times greater. Please review the following PDF: Application of Aluminum Coatings for the Corrosion Protection of Magnesium by Cold Spray

• Hot Corrosion Testing in a Sulfur Environment

Industrial gas turbines are being designed to operate with a variety of fuels such as natural gas, syngas, and fuels derived from gasified coal.  One of the largest impurities in low grade coal is sulfur.  Syngas produced using coal containing high amounts of sulfur results in increased hot corrosion of turbine components. Therefore, in order to evaluate the effects of syngas on the proposed materials, hot corrosion tests were performed on both base alloy materials and environmental coatings.

Hot corrosion testing using the Dean rig testing apparatus was performed under Type I (900 °C) and Type II (705 °C) conditions using NaSO4 or KSO4 in combination with SO₂. Various samples were tested to a total of 100 hours in five 20-hour hot corrosion cycle increments (which corresponds to approximately 1000 hours of burner rig testing).  After each 20 hour cycle at the Type II hot corrosion temperature (705 °C), the samples were cooled to near-room temperature. Subsequently, an additional 3 mg/cm² of sodium sulfate was applied to the sample surface.  This process was repeated until 100 cycles was achieved.  The samples were then analyzed to determine the extent of attack or destabilizing due to sulfur.  The amount of salt penetration and damage was quantified using analytical software.  Corrosion rate/penetration due to gaseous sulfur and corrosion-related failure mechanisms under Type I and Type II conditions was determined.