New technology: Ultra-fast boriding savestime, cleaner6 September 2012

Argonne researchers Osman Eryilmaz (left) andVivekanand Sista (right) recover industrial parts from thelarge-scale ultra-fast boriding furnace after a successfulboriding treatment. The furnace uses an electrochemicalprocess similar to that of batteries to deposit boron onmetal workpieces. Photo credit: Osman Eryilmaz

(Phys.org)—Growing up in Turkey, Ali Erdemir andOsman Eryilmaz would sometimes play with theborax deposits near the mountains by theirhomes—but only later would they discover thatborax would underlie one of their crowningachievements as scientists.

Erdemir and Eryilmaz are part of a team ofresearchers at the U.S. Department of Energy'sArgonne National Laboratory who recently won anR&D 100 Award for a technology that rapidlyconverts metallic surfaces into a hard, durableboride layer. Large-scale ultra-fast boriding can beused to enhance the strength and performance ofmetal or alloy mechanical parts.

Boriding itself is not a new surface hardeningtechnique. Conventional pack-boriding, which isboth labor- and energy-intensive, works by holdingindustrial parts in a powder mix at hightemperatures (1000°C) for 8 to 12 hours. Large-scale ultra-fast boriding, as its name suggests, can

achieve the same boride layer thickness in 15minutes. Furthermore, it produces a denser andmore uniform coating, successfully treats a widerrange of metals and requires 85 percent lessenergy and money than conventional boriding.

For primary investigator Erdemir and his researchteam, the end product was more than they hopedfor. Over three years, the scientists scaled theirultra-fast technique up to industrial productioncapacity. Along the way, they collaborated withBodycote, the world's largest boriding serviceprovider, and researchers at Istanbul TechnicalUniversity. Their work culminated in the successfuloperation of a custom-built industrial-scale furnace,which acts like a fondue pot by holding a moltenborax-based solution into which metal pieces canbe dipped.

Large-scale ultra-fast boriding employs anelectrochemical process similar to that of batteries.Each electrochemical cell contains a positivelycharged cathode, negatively charged anode and aborax-based electrolyte. Samples to be borided areattached to the cathode. When the unit isconnected to a power source, ions flow from theanode to the cathode, depositing boron on thecathode and attached workpieces.

The furnace has three cathodes and four anodes,and holds more than 8,000 pounds of electrolyte. Atfull capacity, it can treat millions of industrial partsper year. "The unit is one-of-a-kind, containing eightlayers and various chambers. It was the majorinnovation of this project," said Eryilmaz, whosupervised the process. It took the scientistsseveral months just to find the correct materials toconstruct it.

The underlying electrochemical mechanism is whatputs the "ultra-fast" in large-scale ultra-fastboriding. While conventional pack-boriding islimited by the diffusion of boron onto the metalsurface, large-scale ultra-fast boriding supplies

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copious amounts of reactive boron to the surface ofworkpieces in a short amount of time. Since theprocess takes minutes rather than hours, it canform thick, dense boride layers that do not crackand chip while boriding takes place. Though large-scale ultra-fast boriding works best for iron- andsteel-based parts, its speed also allows for thetreatment of non-ferrous metals and alloys that areoutside the range of conventional methods.

The process produces a boride layer that adheresstrongly to the base metal and does not come loosewith extreme use, as is sometimes the case withother types of coating. It also extends the life ofmetal parts, so they need to be replaced lessfrequently than they would with other coatingprocesses.

The researchers believe that their technology cantransform boriding from a niche process to one thatreplaces or complements the most commonly-usedsurface engineering and treatment processes."Large-scale ultra-fast boriding can meet theincreasing demands for green, cost-effective andlarge-volume applications in the transportation,manufacturing, aerospace, agricultural, mining andoil-exploration sectors," explained Erdemir. At 18cents to produce a 100-micrometer thick layer onone pound of steel, its cost is lower than that of allmajor competing processes, which start at 34 centsfor the same amount of coating.

Large-scale ultra-fast boriding has the leastenvironmental impact of its competitors. It has thehighest energy efficiency and in many cases saves80 to 90 percent of the energy used in otherprocesses by eliminating a substantial amount oftime and treatment steps. Furthermore, it does notgenerate any in-house greenhouse gas emissions,unlike other processes that produce large amountsof CO2 and other gases, nor does it produce solidor liquid wastes.

The process is much cleaner than pack-boriding,which uses complex powder mixes that give offhazardous emissions and therefore must bereplaced with every boriding run. Large-scale ultra-fast boriding uses the natural mineral borax as itsboron source. As a result, the electrolyte in thefurnace never needs to be discarded, only

replenished when it runs low. For pack-boriding,workpieces must undergo grit-blasting or abrasivegrinding to remove adhering powders. Becauseborax is non-toxic and water-soluble, workpiecestreated with large-scale ultra-fast boriding needonly to be rinsed in water for residue removal.

Furthermore, applications of large-scale ultra-fastboriding could yield tremendous environmentalbenefits. Because the technique creates extremelyuniform layers, it could be used to manufacturewear-resistant, low-friction bearings and gears forwind turbines or engine parts that increase the fueleconomy of automobiles.

Large-scale ultra-fast boriding can also treatagricultural, mining or earthmoving equipment thatcome in frequent contact with dirt, rocks orminerals. Other applications include orthopedicimplants, mechanical seals for industrial pumps,pipes and even armor—the possibilities arecountless and wide-ranging.

Currently large-scale ultra-fast boriding can onlyoccur at temperatures above 750°C. Erdemir andhis team are working on an electrolyte thatoperates at temperatures below 500°C. A lower-temperature operation would extend the range ofmetals that can be treated to include aluminum anda few other non-ferrous materials like magnesium,brass and bronze.

Provided by Argonne National Laboratory

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APA citation: New technology: Ultra-fast boriding saves time, cleaner (2012, September 6) retrieved 26August 2018 from https://phys.org/news/2012-09-technology-ultra-fast-boriding-cleaner.html

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