Technical Article Available from Solar Atmospheres, Inc.
A recent paper has been written with illustrations describing eutectic and sticking in high temperature vacuum furnaces with critical parts, see the complete article.
Introduction
The purpose of this paper is to explain reactions that can occur during a vacuum processing cycle and different methods of preventing these reactions. We will discuss how eutectic compositions can form while heat treating and how diffusion bonding can be a concern to heat treaters when two dissimilar materials are in close contact with each other in high vacuum at elevated temperatures.
To many people, the term “eutectic” is not well understood. The best way to think of a eutectic is a metallurgical meltdown. A eutectic reaction occurs when two components with different melting points and surfaces free of oxides come in contact with each other in the vacuum furnace. This can create an atomic diffusion. For some materials, when a specific atomic composition is reached, they will melt at a temperature much lower than the melting point of the individual metals. If that temperature is reached or exceeded during the heat treating cycle, melting will occur at the contact points. This is referred to as a eutectic melt.
The most common example of a eutectic reaction is with a tin/lead solder. Tin melts at about 450°F, while lead melts at about 620°F. When they are together as two components, the solder melts at 370°F. That is 80 degrees below where tin melts at and 250 degrees below where lead melts.
Another good example in vacuum heat treating is the titanium/nickel eutectic. In this scenario, titanium melts a little above 3000°F, whereas nickel melts at about 2650°F. If you heat treat them in a vacuum furnace, placing the titanium on a typical heat treat fixture such as a grid or stainless steel basket, the two materials would melt at around 1730°F. This could be a disaster if the technician does not understand the eutectic reaction.
We learned a good lesson on eutectic melting a couple years ago when a clean-up run was performed in one of our furnaces at 2400°F without prior removal of a work grid. The high nickel alloy cast fabricated grid was sitting on molybdenum support rods positioned on the furnace graphite support rails.
Figure 1: Eutectic meltdown between the high nickel alloy cast fabrication grid and the molybdenum load rods. This was an expensive mistake, in excess of $150,000.
A form of a eutectic is diffusion bonding, a reaction that occurs well below the eutectic melting point and must be considered when two or more materials are in direct contact.
Diffusion bonding becomes more acute as the mass of the parts in contact increases. In vacuum brazing, a eutectic reaction can be a desirable formation when joining two pieces of metal using brazing filler metals. However, there are times when a eutectic reaction can occur with unintended and often damaging consequences.
Table 1 shows some alloy mating combinations and the eutectic melting points.
Eutectic Barriers
A eutectic barrier is the insertion of a material between the two mating metal surfaces that might be heading for a eutectic melt at elevated temperatures. This barrier material must be capable of withstanding the process’ maximum temperature to be effective.
The most effective barriers are:
- Refrasil cloth or Kaowool blanket
- Thin Ceramic plates
- Ceramic fixtures of different shapes
- Stop–off paints of different types
Refrasil is a clothlike material consisting of more than 96% silica (SiO2) that resists oxidation and most reactive melting. Most Refrasil textiles will not melt or vaporize until temperatures exceed 2650°F.
Kaowool is a good insulation and barrier when used in a blanket form.
Ceramic, high purity alumna can take the form of flat plates or individually designed fixtures to fit a particular application.
Stop-offs are designed to protect metal surfaces from the flow of molten brazing filler metal, or to prevent metal surfaces from adhering or sticking to each other.
The following are illustrations of how barriers are used in actual applications.
1. Kaowool Barrier: Typical load of Titanium logs on Kaowool with graphite fixturing. Processing temperature is 2350°F for 24 hours in high vacuum.
2. Refrasil Cloth Barrier: Separates the bars from the supporting graphite plate. This eliminates the possibility of a eutectic reaction when hardening the bars at 2125°F.
3. Ceramic Plate: Demonstrates the use of a thin ceramic plate to separate the fastening nuts from the graphite support plate. This process is for a sintering procedure to 2500°F.
4. Ceramic Plate: Typical load of nickel iron alloy, MuMetal, fixtured on Alumina sheet with graphite support. Processing temperature is 2150°F.
5. Ceramic Fixture: Using a special ceramic fixture to support the all-thread parts of high speed steel for a hardening cycle at 2100°F. The ribbed ceramic fixture separates the parts from the graphite support plate.
6. Stop-Off Barrier: Typical load of 420 stainless steel molds processed on graphite plate utilizing Wall Colmonoy Inc. white stop–off. Processing temperature is 1900°F.
7. Green Stop–Offs: Typical load of orthopedic implants fixtured with alloy 330 screens utilizing Wall Colmonoy stop–off fixtured in CFC grids. Processing temperature is 2175°F.
8. Other Barrier: Graphite plate supporting the load separated by a high temperature aluminum barrier developed by GMI. This barrier would be similar to using the green stop-off material. This particular hardening process has an upper temperature of 2200°F.
These are just a few examples of how barriers are used to eliminate the possibility of eutectic, or sticking, reactions from forming.
We hope this document illustrates to the vacuum processing personnel how various forms of eutectic melting or sticking can be eliminated and how various types of barriers can be incorporated into a thermal treating process.
For additional information, contact Roger Jones at [email protected], and visit our website at solaratm.com.
Written by: Real J. Fradette, Senior Technical Consultant, Solar Atmospheres, Inc.
Roger A. Jones, FASM, CEO Emeritus, Solar Atmospheres, Inc.
References:
- Critical Melting Points and Reference Data for Vacuum Heat Treating Sept 2010, Solar Atmospheres, Inc.
- Graphite Machine Inc., Topton, PA
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The directory will be accessible both online and through its mobile app. Original equipment manufacturers (OEMs), those in the aftermarket, and product and service providers will benefit from the convenient and easy-to-use Q&A platform. “The road to a vibrant community is based on a balance of both valuable connections and relevant content. Targeting community knowledge is extremely effective to product and service suppliers, and our platform is capable of tapping into that,” continues Charky. “Our Credo challenges us to maintain a laser-targeted focus on resolving end-user issues and empower our members to form reputable profiles as trusted contributors in their respective fields. What’s more, we provide a cutting-edge opportunity to reinvigorate this industry and close the gap with the incoming generation of vacuum heat treaters.”
ABOUT VACUUMFURNACES.COM: VacuumFurnaces.com is where subject matter experts share their know-how and expertise with vacuum furnace end-users in operations, production, training, maintenance, service, support, engineering, and R&D. The platform provides a space for industry professionals to connect over symbiotic knowledge and establish valuable relationships around niche topics with a highly targeted and captive audience. Alan Charky, Founder, VacuumFurnances.com (416) 806-6862. [email protected]”
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The big news for last week was the announcement that Can Eng Furnaces International, one of the largest furnace builders in North America has new ownership (the press release can be found at New Ownership for Furnace Builder Can-Eng Furnaces International Limited | The Monty). Can Eng was founded in 1964 in Niagara Falls, Ontario Canada and has serviced the worldwide heat treating market ever since. While the company is good at many things when we think of them we think mesh belt furnace lines and we are pleased to say that we watched the company introduce the technology into North America.
Going back to the late 1970’s, early 1980’s Can Eng brought mesh belt furnaces into North America through an agreement with a Japanese company that had developed the process. Wally Bamford (owner at the time), Pete Mackenzie, Director of Engineering and John Kay, Sales Manager were absolutely convinced that mesh belt furnaces had tremendous advantages over what was common at the time, cast link belt lines. As we know they were proven correct and today cast link belts have been relegated to a very small part of the market, mainly for large heavy parts only. At the time of introduction a large mesh belt line was 500-1,000 pounds per hour, now it is not uncommon to see lines capable of 6,000 pounds per hour. There is no question that Can Eng has provided more mesh belt lines in North America than any other furnace manufacturer in the world. Having said that though we have visited furnace builders in China who produce one mesh furnace each and every week of the year the vast bulk of which are for the fastener market.
We have a couple of examples of installed mesh belt lines, including a small line in Mexico (above) and a large 6,000 pound per hour line at Metex Heat Treat in Canada below (Metex will be featured on “The Heat Treat Podcast” within the next few weeks). Incidentally we don’t believe any substantial changes are planned for Can Eng although only time will tell.
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Tim Donofrio, VP, Sales Can Eng (Center)
Raman Bawa, Metex, Jordan Montgomery “The Monty”
Winston Heat Treat based in Dayton, Ohio, USA is a third generation family owned commercial heat treater and one which is quite a bit larger than the average commercial shop. The company is a “full service” heat treater in that it offers vacuum heat treating, atmosphere heat treating and nitriding with a strong emphasis on vacuum. Winston was one of the first in the USA to achieve both ISO and NADCAP status.
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Happy Easter, we will resume regular news updates on Monday April 5.
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“Niagara Falls – April 1, 2021; Victor Oreskovich, Owner of JTL Integrated Machine Ltd. (JTL), and Trenergy Inc. (Trenergy), is pleased to announce the recent acquisition of Can-Eng Furnaces International Limited. (CAN-ENG).
Mr. Oreskovich has expanded his family of companies to further enhance and leverage each group’s ability to include customized engineered solutions. According to Mr. Oreskovich, “As a mechanical engineer born and raised in Niagara, I have always had great admiration for CAN-ENG’s technical expertise, and the level of quality and creativity provided by their products which are installed around the world”. With the addition of CAN-ENG, the combined resources will increase to over 250 associates, operating at four separate locations, consisting of a total of over 300,000 ft2 of available floorspace, outfitted with the most modern manufacturing capabilities. With this potential, CAN-ENG will be perfectly positioned for strategic growth and development activity in thermal processing and heat treatment markets previously not explored.
About Each Group
CAN-ENG is a leading global designer and manufacturer of thermal processing equipment for ferrous and non-ferrous metals. Since 1964, CAN-ENG has focused on the development of high volume, automated industrial furnace systems for challenging applications. Over these years, CAN-ENG has gained an international reputation for design innovation, quality workmanship and dedication to service. CAN-ENG’s highly innovative furnace systems provide the latest advancements in energy saving technology and automation. The Company finished 2020 with a large backlog, bolstered by a high order intake well above plan for the operating year.
JTL is one of the largest machining facilities and fabrication shops in North America serving a number of industries including automotive, transportation, renewable energy, power generation, oil and gas, air compression, metal processing and mining. Established in 1964, JTL offers full-service precision component manufacturing capabilities that include the largest CNC machines available, heavy metal fabrication, assembly, surface finishing, high accuracy laser inspection and testing metrology capabilities.
Trenergy is a global supplier of infrastructure critical, code specified pressure vessels, drums, superheaters, economizers, waste heat boilers, heat exchangers, gas coolers and moisture separators. Operations at this facility began over 100 years ago, as the Foster Wheeler Corporation. Trenergy today integrates a team of skilled craftsmen supported by modern automatic machinery and production control techniques which are complimented by an extensive array of non-destructive examination procedures. These features allow Trenergy to be recognized as one of the world’s most trusted suppliers to the nuclear field, refineries, power plants, chemical sector and structural building and bridge constructors. For further information please contact [email protected].”
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In keeping with the spirit of “April Fools Day” we posted a news item yesterday evening entitled “Price Gouging or Price Reality? Anhydrous Ammonia Prices Climb 60% Since Fall”. While there was a grain of truth to the news item it is not in the main correct. Yes ammonia is widely used in the heat treatment industry, mainly in nitriding applications and yes some ammonia pricing has increased but not to a significant degree, at least for heat treaters. Recently several individuals have approached us asking if ammonia pricing was increasing which prompted “The Monty Heat Treat News” to look into it. It turns out that farmers are seeing enormous increases in fertilizer pricing because the cost of Anhydrous Ammonia has increased dramatically in a short period of time, however this is not the case with ammonia supplies being used by heat treaters.
Ammonia is sold as a liquid and evaporated into a gas and priced per pound. Normally heat treaters have a 1000 gallon tank or 2 1000 gallon tanks and the current price is roughly $.85 USD per pound. We checked with the major supplier in the industry “Tanner Industries” and their response was that there have been some modest increases recently but just that-modest which leads us to believe that the granular ammonia used in fertilizer is different than the liquid ammonia used by heat treaters. So that is our April Fools day joke which proved to be a learning curve for the team at “The Monty Heat Treat News”.
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The Vector® 2-bar quenching unit from SECO/VACUUM is equipped with high vacuum diffusion pump and convection heating. It meets class 2 requirements per AMS2750F (temperature uniformity +/- 6°C (+/- 10°F). It will be installed in the company’s Center of Excellence and will be used to heat treat 3D printed parts.
This expansion of capabilities continues the relationship that SECO/WARWICK Group has with the manufacturer, who has been expanding their heat treat capabilities with the Group for the last 10 years at locations in Poland, Indonesia, Singapore, France, and the US.
Maciej Korecki, VP of the Vacuum Business Segment at SECO/WARWICK Group said that this is a confirmation that the company continues to deliver “products that not only fulfill but exceed their needs.”
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The Nitrex Webinar entitled ‘Improvement of Gear Life & Performance Through Controlled Nitriding” is now concluded and according to this report from Nitrex attracted a great deal of attention;
“Our recent webinar ‘Improvement of Gear Life & Performance Through Controlled Nitriding’ was a great success – attracting a truly global audience of gear manufacturers, suppliers, and related service providers eager to learn first-hand how #nitriding is an effective way to improve the tribological properties of gears for unmatched reliability, performance, and longevity. The event drew more than 275 registrants and scores of questions were posed to presenter Jack Kalucki and moderators, Michel Frison and Tom Cooper. A big #THANKYOU to all who attended yesterday’s event. Your feedback and positive comments are greatly appreciated.”
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Today “The Heat Treat Podcast” talks Low Pressure Carburizing (LPC) with Mr. Dennis Beauchesne of ECM. Dennis has had a long and distinguished career in the heat treatment industry and was recently named as one of the “Most Influential Individuals in the North American Heat Treat Industry” by “The Monty Heat Treat News”.
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