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Case Hardening Steel and Metal

Improvement of Tribological Properties Through Nitrocarburizing 

Structure, Hardness and Depth of the Nitrocarburized Layer.-case hardening-

During nitrocarburizing, a two-part surface layer is formed, initially an outer compound layer, followed by a diffusion layer below it. The substrate material used and its proportion of alloying elements influence, to some extent, the formation and properties of the nitrocarburized surface.

Case Hardening Compound Layer

The nitrogen-rich inter-metallic compound layer mainly contains iron-carbonitrides and, depending on the type and proportion of alloying elements in the base material, special nitrides.

Case Hardening : A unique feature of salt bath nitrocarburized layers is the monophase _-Fe_N compound layer, with a nitrogen content of 6-9% and a carbon content of around 1%. Compared with double phase nitride layers which have lower nitrogen concentrations, the monophase _-Fe_N layer is more ductile and gives better wear and corrosion resistance by improvement with case hardening. In metallographic analysis the compound layer is clearly definable fron the diffusion layer as a lightly etched layer. A porous area develops in the outer zone of the compound layer. The case hardness of the compound layer measured on a cross-section is around 700 HV for unalloyed steels and up to about 1600 HV on high chromium steels. Treatment durations of 1-2 hours usually yield compound layers about 10-20 _m thick (0.0004 - 0.0008"). The higher the alloy content, the thinner the layer for the same treatment cycle. Fig. 2 shows the relationship of layer thickness to treatment time with nitrocarburizing temperature of 580�C (1057�F).

Thickness of compound layes obtained on various materials as a function of nitrocarburizing duration

Case Hardening : Diffusion Layer

The nitrogen penetration into the diffusion layer provides for improved fatigue strength. Depending on the initial structure and composition of the core material, the nitrogen in the diffusion layer is dissolved in the iron lattice and/or precipitated as very fine nitrides.

Influence of chromium on diffusion layer hardness and total nitration depth in various 0.40-0.45% carbon steels

Case Hardening With unalloyed steels, the nitrogen is dissolved in the iron lattice. Due to the diminishing solubility of nitrogen in iron during slow cooling, _'-Fe4N nitrides are precipitated in the outer region of the diffusion layer, some in form of needles, which are visible in the structure under the microscope. If cooling is done quickly, the nitrogen remains in super-saturated solution. With alloyed steels which contain nitride-forming elements, the formation of stable nitrides or carbonitrides takes place in the diffusion layer independent of the cooling speed. With increasing alloy content of the steel, the diffusion layer is thinner for identical nitrocarburizing parameters. However, with their higher level of nitride-forming alloying elements these steels have a greater case hardness. Fig. 3 illustrates the influence of chromium on the hardness and depth of the diffusion layer in steels with a carbon content of 0.40 - 0.45% after 90 minutes treatment at 580�C (1075�F). Total nitrocarburizing depth shown in Fig. 4 is the distance to the point where the hardness of the nitride layer is equal to the core hardness. After a 90 minute treatment the total nitrided depth is about 1.0 mm (0.040") on unalloyed steel, but barely 0.2 mm (0.008") on a 12% Cr steel. (See Fig. 4.)

Total nitrided depth on various materials resulting from nitrocarburizing

Fig. 7 shows the coefficient of friction both under dry conditions and after lubrication with SAE 30 oil, measured by an Amsler machine. All samples were lapped to a roughness of R_ = 1_m after their respective surface treatments and before testing. Without lubrication the nitrocarburized QP had the lowest coefficient of friction, being less than half of that of the hard chrome or case hardened surfaces. The lowest friction level occurred when nitrocarburized QPQ is lubricated. It is 3-4 times lower than that achieved with the chrome or martensitic surfaces.

Coefficient of friction values for various surface layers, with and without lubrication. 

Case Hardening SNC = salt bath nitrocarburized

These results show the direct effect of increased oxidation as it relates to friction on the surface of the nitrocarburized samples. The QPQ sample, with its extra post-oxidation step, has a much higher friction value than the QP specimen, which had part of its original oxidation in the compound layer removed by lapping. However, with this variant, due to the fine microporosity in the QPQ sample which causes the lubrication to adhere better to the surface, this option gives the lowest friction value.

If a uniform running behavior is required the QP process is appropriate. Lubrication has only a slight influence on the coefficient of friction because the oxide layer of the outer surface was removed during the polishing operation.

It has been determined that, unlike with chrome surfaces, the coefficient of friction of nitrocarburized QP and QPQ treated surfaces remains constant, even at varying sliding speeds.

The intermetallic stricture of the compound layer, which contains epsilon iron nitride formed during nitrocarburizing, is extremely resistant to adhesive wear and scuffing. Fig. 8 shows the scuffing loads of gears made from various materials (6). It was established by applying increasing pressure to the flank tooth until galling occurred. Austenitic steel containing 18% chromium and 8% nickel had the lowest resistance to galling, however, after nitrocarburizing its resistance was raised almost five-fold. The performance with SAE 5134 was about tripled. Even SAE 5116, which had already been carburized, more than doubled the scuffing load it could withstand through the compound layer built by the nitrocarburizing treatment.

Scuffing load limit of gears.
SNC = salt bath nitrocarburized

New Fastener Doubles as Crack Sensor

Alcoa focuses on proprietary aircraft fasteners for composite metal and carbon structures.

Doug Smock, Contributing Editor, Materials & Assembly -- Design News, March 30, 2011

Working with Stanford researchers, Alcoa is developing aircraft fasteners that also function as sensors capable of detecting crack propagation in multilayer composite structures.

The technology could reduce inspection frequencies for wing stringers by one-half. Fatigue cracks forming at fastener holes are a common form of airframe damage.

In the invention, a fastener couples layers of a multi-layer structure together via an opening that traverses the structure. A sensor circuit is inserted into the opening with the fastener, inducing an electrical response in a portion of the multi-layer structure adjacent to the opening. If the structure surrounding the fastener hole is damaged, the electrical response is slowed, indicating a failure.

A new fastener can sense crack propagation in composite aircraft structures. Source: Alcoa

In one example of the technology, a sensor film is embedded on the shank of an aircraft fastener, such as a 1.5 inch shank fastener from Alcoa Fastening Systems. An eddy current is applied to the sensor. The sensor's circuit is established by a coating applied to the fastener and the conformable film.

Alcoa told Design News that the specific materials' technology is proprietary.

The sensor circuit includes an active conductor to induce the electrical response, and a passive conductor to sense the induced electrical response. The active and passive conductors are wound around an outer diameter of the mechanical coupler to form an alternating winding pattern of active and passive conductor lines.

"When you plug this in, you can see if there is a crack and if it has propagated," says Bill Christopher, executive vice president of Alcoa.

Stanford University developed the structural health monitoring (SHM) technology under a research grant sponsored by Alcoa.

Alcoa's SHM system can be used for aluminum aircraft structures as well as hybrid structures that combine carbon fiber-reinforced composite and aluminum. For example, the SHM system can be applied to the joint between aluminum ribs and carbon fiber reinforced wing skins.

Pre-production prototypes of Alcoa's SHM system are currently being tested with select customers for commercial applications.  Alcoa plans to complete comprehensive testing with select customers before SHM reaches full production.

The new fastener is an example of a focus on aircraft assembly technology for Alcoa since it acquired fastener specialist Huck in 2000. In 2002, Alcoa acquired Fairchild's fastener business and formed Alcoa Fastening Systems. Other acquisitions followed, and Alcoa is now the world's largest producer of aircraft fasteners. Alcoa is ramping up fastener production capability in China and other rapidly developing countries.

"Our fasteners aren't the nuts and bolts you buy at Lowes or Home Depot," Christopher told analysts in New York last month. "To give you one example, we have developed a one-inch diameter titanium fastener used on the 787 and A350 that can support the weight of 50 Toyota Camrys."

Alcoa's competitive strategy focuses on design engineering.

"When composites were starting to emerge, we made the decision to be the industry leader in joining dissimilar materials," says Christopher. "One issue that we knew would come up was lightning strike. When you drill through metal, you get a nice hole. With composites, it's serrated."

Voids created by uncut fibers or resin are referred to as machining-induced micro texture. They can trap excess sealant, inhibiting close electrical contact between the fastener and the composite structure. Machining-induced micro texture is associated with arcing between the fastener and the composite structure during lightning strike tests.

Lightning protection of composite structure is more complex because of the high resistance of carbon fibers and epoxy, the multi-layer construction and the anisotropic nature of the structure.

Inherent conductivity of metallic fasteners coupled with the large number of fasteners used in planes creates a high probability of lightning damage on fasteners.

"So we had to develop a sleeved fastener that allows you to have a perfectly close hole," says Christopher.

Conforming fasteners decrease the voltage drop across the interface and reduce the dielectric effect caused by the sealant, minimizing the possibility of arcing between the sleeve and the composite panel. 

Alcoa also developed the Ergo-Tech next-generation fastening system that can be installed by a single person or robotic system instead of two people. The key feature is advanced low-torque installation tooling that reduces strain on installers, making it more compatible with robotic systems, and reducing installation time and cost.

More than ninety percent of Alcoa's assembly systems are specialty structural fasteners and 55 percent of them are either patented or proprietary.

Watch This Robot Crawl on a High-Voltage Power Line

Inspection of high-voltage power lines is costly, difficult, and a dangerous job even for skilled workers. Which means it's the perfect job for a robot.

We first wrote about Expliner, an incredible inspection robot that balances on power lines like an acrobat, more than a year ago. Since then, HiBot, the Japanese company that developed Expliner, has gone on several inspection jobs, remote operating the robot as it crawls on 500-kilovolt live lines.

The company is now gearing up to deliver the robot to customers, first in Japan, and later abroad as well.

Expliner is like a wheeled cable car that rolls along the upper pair of bundled cables. In addition to its manipulator arm, it carries laser sensors, to spot corrosion or scratches, and a high-definition camera, which records details of bolts and spacers far more effectively than even a human worker.

HiBot says that Expliner is a semi-autonomous robot.

"There is always a human in the control loop, but the basic repetitive tasks are automated," says Michele Guarnieri," a HiBot co-founder. "Tasks that require a high degree of precision, like maintaining balance or moving parts to a certain angle, are also automated."

He explains that the robot can inspect up to four cables simultaneously, and software automatically checks all recorded videos and alert users about potential damages or problems on the lines.

HiBot has recently released a new video that shows off the robot's capabilities, including being able to go over cable suspension clamps through a series of acrobatic maneuvers using a dangling counterweight to shift the robot's center of gravity. Watch: 

HiBot, which spun off from the laboratory of Tokyo Tech roboticist Shigeo Hirose (known for his incredible snakebots), has recently won an award for the Expliner robot from Japan's Ministry of Economy, Trade, and Industry.

And if you're wondering, "Expliner doesn't fall," claims Guarnieri. "It's equipped with safety devices that prevent the robot from falling, even in case of strong winds."

Images and video: HiBo

Wire Processing: The Future of Wire

New technologies may replace traditional wiring harnesses. Automotive, aerospace and military manufacturers have relied on wiring harnesses for decades. But, as products grow more complex and weight reduction becomes more critical, engineers are eager to find an alternative. Evolving technology, such as carbon nanotubes, fiber optics and printed electrical systems, may provide the backbone of future electrical distribution systems in cars, trucks, locomotives, aircraft and other vehicles. Despite recent price hikes, traditional copper wire bundles will probably continue to be used for years to come, due to outstanding electrical performance and ease of use. Copper wire is a safe, proven commodity that engineers are comfortable with. In addition, manufacturers already have large amounts of money invested in wire processing equipment, such as strippers, cutters, crimpers and welders. “Wire is still the best way to go for many applications,” says Chris Burns, director of electrical-electronic architecture engineering at Delphi Corp. “It has the best conductivity you can get. That’s why we’ll still have a need for traditional systems for a long time to come.” But, there’s a limit on how far wire can go. For instance, Delphi engineers are using more 26 AWG wire to reduce weight and space in some automotive applications. And, some medical device manufacturers currently use wire as small as 40 AWG, which boasts a 0.08 millimeter diameter. While pushing the boundaries of thin-gauge wire is possible, there’s little room for error as it becomes exceedingly difficult to route tiny wires and cables in an efficient package. Weight reduction is also a growing challenge to many manufacturers, especially in the aerospace industry. For instance, the Boeing 747 contains more than 135 miles and 4,000 pounds of wire. Engineers are scrambling to reduce the size and weight of wiring harnesses as they develop more fuel-efficient aircraft. Nanotech Takes Off Enlarge this picture Carbon nanotube wire and shielding are copper-coated to enable soldering of connectors.Photo courtesy Nanocomp Technologies Inc. The aerospace industry is leading the charge to develop alternatives to traditional wire and cable. One technology that has tremendous long-term potential is nanotechnology. Carbon nanotubes (CNTs) are already being used for some military applications that require smaller and lighter wiring harnesses, such as unmanned aerial vehicles and satellites. Carbon nanotubes have a strength-to-weight ratio that is not matched by any other known material. Engineers at Nanocomp Technologies Inc. have figured out how to turn them into wiring that has very high tensile strength, highly efficient electrical conductivity, electromagnetic interference (EMI) shielding capabilities and extreme light weight. During the past few years, Nanocomp has been involved in several research projects with the U.S. Air Force and Northrop Grumman Aerospace Systems. “The nature and importance of these projects demonstrates the unique potential of our material as the basis for creating game-changing, yet cost-effective replacements for traditional aerospace components,” says Peter Antoinette, president and CEO of Nanocomp. “We’ve proven that the performance of CNT wiring is superior to that of copper for high-frequency applications, with dramatic weight savings.” There are several benefits to using CNT-based wiring as an alternative to traditional solutions, including: Weight savings. “By using [our] CNT tape product as a replacement for conventional copper and aluminum cable shielding, aerospace manufacturers can achieve additional savings of up to 50 percent, while maintaining comparable or better electrical performance,” claims John Dorr, vice president of business development at Nanocomp. “In the case of center conductors, [weight savings can be] as much as a 10 percent.” Copper competitiveness. “[Our] CNT materials are significantly lighter than traditional copper wiring technology,” says Antoinette. “[The material weighs only] 0.4 grams per cubic centimeter, as compared to copper, which is nearly 9 grams per cubic centimeter. In addition, especially at higher frequencies, CNT wiring exhibits comparable or better conductivity than conventional copper.” Reliability. “Flex testing has demonstrated [that] CNT conductors exceed flex limits of copper by several orders of magnitude, offering a more reliable solution for many wiring applications,” Dorr points out. Temperature stability. “CNT wires typically demonstrate more stable resistivity characteristics as a function of temperature, which is not the case for copper, particularly as higher temperatures come to bear,” explains Dorr. CNT’s also do not corrode like conventional copper wires, which can alleviate early failures due to overheating. Nanocomp engineers are currently working with Northrop Grumman to develop next-generation CNT cabling and tapes that are “intended for near-term insertion into aircraft as a replacement for conventional copper-based wires and cables.” “The two-year program, entitled the Nanocomposite Connector Partnership, [aims] to define cable design parameters and replicable manufacturing processes,” says Don DiMarzio, integrated product team leader for emerging concepts at Northrop Grumman Aerospace Systems. “The end result will be an optimized manufacturing platform designed to produce efficient and cost-effective materials, so that transition and broad-based implementation of carbon nanotube-based conductors can take place,” claims DiMarzio. “We believe this initiative will result in a true 21st century solution to vastly improve the weight and fuel efficiency of modern aircraft, for sustainable cost and energy savings.” Carbon nanotube sheet and yarn materials are wound on spools like traditional wire. Nanocomp uses a combination of custom-built and off-the-shelf hardware, along with proprietary processes, to manufacture its CNT sheet and wire products. “We envision widespread adoption [of the technology in the aerospace and military industry] in less than five years, likely sooner,” says Dorr. To anticipate growing demand, Nanocomp is in the process of moving into a new, large-scale manufacturing facility. Despite numerous benefits, widescale use of nanowire will be hampered by capacity and cost challenges. “Wire solutions require relatively high levels of manufacturing capacity compared to other applications for CNTs,” notes Dorr. “In addition, most interconnect solutions are price-sensitive, as they are often more of a commodity than a specialty solution. “A second challenge is implementing CNT wiring solutions for DC power applications,” adds Dorr. “Today, CNT wiring is better suited for RF-signal solutions. Copper continues to outperform CNTs at low frequencies.” Automotive engineers also see tremendous potential for CNT wires. “It has some intriguing possibilities,” says Burns. “Delphi is expanding our R&D efforts on nanotechnology.” The Honda Research Institute USA Inc. has been studying the topic for several years, working in conjunction with engineers at Purdue University and the University of Louisville. “Microscopic carbon nanotubes a hundred thousand times thinner than a human hair may have the potential to transport electricity faster and over greater distances with minimal loss of energy,” claims Hideaki Tsuru, project director. “[Our] findings open new possibilities for miniaturization and energy efficiency, including . . . electrical cables,” adds Tsuru. At Honda’s lab, CNTs are grown on the surface of metal nanoparticles, taking the cylindrical form of rolled honeycomb sheets with carbon atoms in their tips. “When these tiny carbon nanotubes exhibit metallic conductivity, they possess extraordinary strength compared to steel, higher electrical properties than copper, are as efficient in conducting heat as a diamond and are as light as cotton,” Tsuru points out. Honda has already achieved a success rate of 91 percent metallic conductivity. Fun With Fiber Enlarge this picture Carbon nanotubes can be grown on the surface of metal nanoparticles, taking the cylindrical form of rolled honeycomb sheets with carbon atoms in their tips. Red and pink indicates metallic properties. Illustration courtesy Honda Research Institute USA Inc. Fiber optic technology is not as sexy as carbon nanotubes, but it also has potential to replace traditional electrical wiring in some products, such as airplanes and helicopters. Light-transmitting cables weigh less and take up less space than copper wiring in aircraft. They also have better immunity from strong radio signals and lightning, are free from short circuit arcing and can carry more electronic signals. A fiber optic control system could result in lighter, more fuel-efficient airplanes with more reliable control and monitoring systems. According to engineers at NASA’s Glenn Research Center, weight and fuel savings in aircraft engineered with fiber optic control systems could be substantial, compared to designs using traditional copper wiring. Long copper cables not only weigh more than fiber optics, but also must be shielded with insulation to protect other aircraft systems from signal leaks. “Fiber strands the size of a hair can convey hundreds of high-speed signals, replacing bulky and heavy copper cables,” says Ronald Bishop, president of Bishop & Associates Inc., a market research firm that recently published a new report on fiber optic connectors in military and commercial applications. “The ability to transmit signals many kilometers without amplification was immediately adopted by the telecom industry in long-haul applications, but wide market adoption in additional market segments has stumbled due primarily to cost.” The idea of using fiber optics for aerospace applications is not new—NASA engineers studied the concept in the late 1980s and early 1990s. They discovered that digital signals would travel more quickly between locations in an aircraft equipped with fiber optic controls because fiber optic cables do not have the built-in resistance that copper cables have to electricity running through them. But, fiber optics failed to catch on for many non-telecom applications. “The immanent demise of copper has been predicted many times over the years, but a combination of advanced chip technology together with improvements in design for signal integrity has allowed engineers to find ways to expand the practical bandwidth of copper,” Bishop points out. “Costs associated with the required electro-optic conversion process, together with connectors that require skilled technicians to successfully terminate, discouraged broad market conversion to fiber. “As we reach system requirements for [unlimited high-speed bandwidth and multiple] channels, fiber is again gaining attention as a viable alternative,” claims Bishop. “Fiber optic links are beginning to approach cost parity with copper in many applications.” Printable Wiring Enlarge this picture The performance of carbon nanotube wiring is superior to copper for high-frequency applications, with dramatic weight savings.Photo courtesy Nanocomp Technologies Inc. In the near future, wiring harnesses, connectors and other electrical components may be printed with the touch of a button. Printed electrical systems are an offshoot of printed electronics, a fast-growing field. Printed electronics are based on flexible substrates of functionalized polymer films that are less than 1 millimeter thick. “The market potential for printed electronics is huge,” claims Wolfgang Mildner, chairman of the Organic and Printed Electronics Association (OE-A). “Thinness, flexibility, robustness and easy integration are the competitive advantages of this new technology.” Klaus Hecker, OE-A’s managing director, believes there could be numerous applications for the technology in the auto industry. “By mid decade, there will be fully integrated, smooth and aesthetically pleasing interiors with embedded displays and switches,” he predicts. “They will show only when needed and be activated by slight touch. “This will also pertain to the exterior: very thin, yet brilliant organic LED backlights [will be] directly glued to the car body,” Hecker points out. “Printed conductors [will] connect with the car’s electrics. [There will be] no screws, no parts protruding to the densely packed innards.” “Completely printed and laminated replacements for instrument clusters and wiring will save weight, cost and space in cars,” adds Peter Harrop, chairman of IDTechEx, a consulting firm specializing in printed electronics. “Wireless sensors and actuators will also save wiring in future vehicles and gradually be printed themselves.” Conductive inks will allow manufacturers to print some electrical systems. “The technology has the potential to be applied to composite panels used in aircraft fuselages and automotive bodies,” says Stan Farnsworth, vice president of marketing at NovaCentrix, which has developed a copper ink called Metalon. “True copper inks are available for screen, flexographic or gravure application,” adds Farnsworth. “In conjunction with our PulseForge technology, these inks can be applied to substrates such as plastic films and even paper.” The PulseForge tools use brief, extremely high-powered pulses of light from custom lamps to sinter inorganic inks and films at room temperature. The combination of Metalon and PulseForge allows conductivity requirements to be met using thin, flexible substrates. Most substrates remain unaffected because of the very short pulse duration. “There’s been a lot of interest in this process,” says Farnsworth, a mechanical engineer. “Most of the focus has been in the packaging industry, but it also has a lot of potential to replace traditional wiring in many industries. We’re currently working with some aerospace and military manufacturers. “Printing is an additive process,” Farnsworth points out. “You put it where you want it. You’re not adding a wire after the fact. It allows you to get away from traditional wiring harness restrictions, such as size and weight. Printable electrical systems can also eliminate several design and assembly steps, which reduces cost and complexity. And, we use water-based inks to achieve a green manufacturing process.” However, Farnsworth says copper ink technology still needs more development. For instance, “we’re currently at about half the conductivity of wire,” he explains. “We’re addressing issues relating to moisture, temperature and humidity.” A Learn more about the future of wire by clicking www.assemblymag.com and searching for these articles: A World Without Wire? Wireless Technology May Let Robots Go Free by Austin Weber March 30, 2011

The Tool: "Behavior Modeling"

Behavior Modeling is a very powerful tool that Leaders Need to Master if they really want to get up high! It is a clear message of "Do as I Do" instead of the authoritarian "Do as I Say". When we show people our respect and do ourselves in an emphatic show of humbleness and friendship something that will make their areas nicer, more comfortable, safer, world-class; people will gladly follow the example, no words needed.

      

     This strategy works in any environment, it is like magic at home too.

Leadership is always better by example than by mandate. If you want people to enjoy doing what they do to comply with their responsibility, show them you are willing to do it yourself. This improves the image of the leader and makes the followers feel more comfortable and proud. That is the best status of a team that will be ready to support any new initiatives and succeed in each simple or complex task.

Behavior Modeling is among the many skills that we include in our
Management Through Leadership training products.

Rahul KP