Grantee Research Project Results
Final Report: Pollution-Free Process for Surface Protection
EPA Contract Number: 68D98148Title: Pollution-Free Process for Surface Protection
Investigators: Tramel, Terri L.
Small Business: Surface Treatment Technologies Inc.
EPA Contact:
Phase: I
Project Period: September 1, 1998 through March 1, 1999
Project Amount: $69,667
RFA: Small Business Innovation Research (SBIR) - Phase I (1998) RFA Text | Recipients Lists
Research Category: SBIR - Pollution Prevention , Pollution Prevention/Sustainable Development , Small Business Innovation Research (SBIR)
Summary/Accomplishments (Outputs/Outcomes):
Purpose of Research:
Chromium coatings are found in a wide range of applications and take advantage of the unique combination of adhesion, hardness, corrosion, and wear resistance. Existing and planned environmental legislation severely restricts the use of process chemicals containing hexavalent chromium ions and substantiates a need to develop alternative coatings. The Pollution Prevention Act has provided both problem definition and initiatives for action to attack pollution prevention via "source reduction" of hazardous substances, pollutants, and contaminants entering waste streams or otherwise released into the environment. The problem addressed in this research is categorized under "metal finishing," one of the six industry sectors under EPA's Common Sense Initiative. From an industry perspective, it is becoming increasingly difficult and expensive to control plating residuals and comply with disposal requirements. Further, chrome plating does not always provide the desired protective qualities. For example, the mechanical bond to the substrate permits delamination under some wear conditions. Chrome plating of irregular contours results in excessive plate thickness close to the electrodes and minimum plate thickness further away. Further, chrome plating often does not provide the wear characteristics the user desires, but it has been the best available solution.
Alternatives to hexavalent chrome plating are most easily broken down into near term solutions and longer term solutions. Most near term solutions are modifications of current processes by simply substituting a new material or modifying a current process. Longer term solutions often require more sophisticated equipment, workers with new skills, and as yet mostly uncommercialized processes. This research has the objective of replacing chrome plating with an environmentally friendly process for a variety of applications. The research must demonstrate that the proposed metal finishing process equals or exceeds hard chrome plate characteristics for appropriate technical properties (primarily wear and/or corrosive protection) and can be applied without environmental pollution.
Work Performed:
The research takes advantage of a newly invented surface alloying process (patent pending) called Laser Induced Surface Improvement, or LISIsm. The technology was invented at the University of Tennessee Space Institute and is licensed by ST2. Previous research has shown that a wide variety of precursor materials can be alloyed into the surface of a wide variety of substrate metals with little or no waste stream or effluent concerns.
The basic goals of this Phase I research were to identify surface alloy compositions which provide good wear and/or corrosion protection and to adapt the LISIsm alloying process to permit formulation of these surface alloys. Since the premise is a process to replace chrome plating, the LISIsm formulated surfaces were compared with chrome plated surfaces via similar test regimens, with the objective of providing equal or superior surface qualities. The "coated" samples were subjected to laboratory wear testing (ASTM G-65 and ASTM G-76), salt-fog chamber corrosion tests and hardness tests. Other evaluations used optical and electron microscope data to determine microstructure and coating quality. Effluent gasses were captured during processing and analyzed. There was no requirement to demonstrate the metallurgical bond of the LISIsm generated surface (i.e., vs. the mechanical bond of chrome plating) since the results of prior experiments had been accepted. Finally, environmental friendliness in manufacture was to be confirmed.
In coordination with industry, it was agreed that two substrate materials would satisfy the initial research objectives; i.e., 4140 steel for corrosion and wear enhancement, and D2 steel for wear enhancement. Flat plate samples of 4140 and D2 steel were LISIsm-treated with several alloy mixtures of metals and/or ceramics. The industrial participants provided advice on technical requirements and furnished chrome-plated samples that were used for the comparative tests. Each new alloy composition and/or change in substrate materials, as well as a change in alloy thickness, requires analyses of material properties and an iterative experimental process to achieve the desired heating/cooling rates and alloy microstructure. Small departures from the database began the experiments, but final compositions were completely new formulations.
Results:
Over 50 combinations of precursor materials and LISIsm processing parameters were applied to 4140 and D2 steel. These samples were subjected to wear tests, corrosion tests, hardness tests and microscopic analyses. While data has been recorded and will be useful for future applications, the Phase I results focus on two LISIsm-processed samples to prove the hypothesis and illustrate readiness for further demonstration of the technology. A 100% chromium precursor was alloyed into 4140 steel substrate and a 70 TiC-10WC-20Fe precursor was alloyed into both 4140 and D2 substrates.
Chrome-rich alloyed LISIsm surfaces on 4140 steel performed similar to the hard chrome-plated surfaces in both the ASTM G-65 and G-76 wear tests. Alloy thickness on the various samples varied between 180-220 microns. Alloy chrome content averaged 85 wt% on the surface. These treated samples also performed well in the corrosion tests, behaving like stainless steel. Titanium carbide alloyed into the 4140 showed a 24% improvement over chrome plate in the G-65 test results (G-65 uses sand as the abrasive element). Titanium carbide was alloyed into the D2 steel and reduced wear in G-76 (metal wear wheel) tests by 76%. Thus for some applications, it is not necessary to use any chromium to replace chrome plating. Microhardness indents at the alloyed surface gave hardness values that were lower than those for chrome plate, although the TiC/D2 was very close [962 vs 1012 Hk(500g)]. It is noted that hardness and wear do not necessarily correlate (i.e., some types of wear may be better using a "softer" material). While these laboratory tests are not likely to duplicate any particular operational environment, they do demonstrate that LISIsm generated surfaces offer good potential for replacing chrome plated surfaces.
A primary advantage of LISIsm over plating techniques is that large quantities of hazardous material are not produced. When considering the different materials utilized in this study for replacement of chrome plating, chromium is the only material which reduces to other dangerous forms. The other materials exhibit the same safety hazards as any non-pyrophoric powder metals. However, hexavalent chromium (Cr+6) is a noted hazardous material, and gas-sampling trials have been made to determine the production rate of Cr+6 during LISIsm operations. Note that this is a concern only in cases where chromium is used in the precursor. LISIsm process effluents were captured over the course of several hours of standard operation. These test samples were analyzed using gas chromatography, and the results show that production of Cr+6 as a result of LISIsm processing is about two orders of magnitude below acceptable OSHA limits.
Competitive Advantages:
The LISIsm technology joins a host of other surface protection technologies that are competing for a multi-billion dollar market. However, LISIsm offers a combination of technical features that are unique; i.e.;
- Environmentally friendly application (no harmful effluents or residuals).
- No special environment required for processing (e.g., a vacuum).
-
Ability to create alloys of choice on metal surfaces, including non-equilibrium
alloys not possible by other means.
- Ability to process inside pipes and
small enclosures (energy transfer via fiber optic cable).
- Metallurgical
bond to the substrate that will not separate from physical abuse or thermal
cycling.
- Fine grain and nonporous surfaces provide protection with thin
layers (saves costly materials).
- Ability to LISIsm-treat only wear areas
(i.e., versus the entire component).
- Little or no surface preparation
before treatment.
- Minimum heat input into the substrate reduces
heat-affected zone. Laser can be operated in continuous or pulsed mode.
While other surface coating techniques can claim one or more of these qualities, LISIsm uniquely provides combinations of interest for some applications. ST2 is working with four industries that will be part of a Phase II SBIR program and will introduce LISIsm-treated products into field demonstrations and the market place.
Supplemental Keywords:
RFA, Scientific Discipline, Air, Toxics, Waste, Sustainable Industry/Business, hexavalent chromium waste, hexavalent chromium, Chemical Engineering, cleaner production/pollution prevention, Environmental Chemistry, Analytical Chemistry, Chemistry and Materials Science, Engineering, Chemistry, & Physics, 33/50, Environmental Engineering, laser induced surface improvement, cleaner production, dry plating, environmentally conscious manufacturing, green design, hard chromium plating , waste minimization, waste reduction, environmentally benign coating, emission control technologies, chromium & chromium compounds, Chromium, clean technology, chromate substitution, alternative materials, emission controls, metal finishing, metal plating industry, chrome plating, coating processes, production processes, chromium plating, alternative metal finishing, innovative technology, emission reductions, air emissions, coatings, industrial innovations, pollution prevention, emissions contol engineering, metal plating, alternative metal coating, green technologySBIR Phase II:
Pollution-Free Process for Surface Protection | 1998 Progress Report | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.