Pack Boriding Research Articles

Property enhancement of diffusion borided layers by laser treatment

Tribological properties such as abrasion and erosion resistance of boride coatings on steels have been proven to be outstanding when compared with conventional hardening techniques, e.g., carburizing and nitriding. Pack boriding is a relatively simple and economical technique among all the methods available for boriding. A single phase Fe2B layer is desirable in the boride coating for its superior performance and this can be achieved in several ways. However, the boride coating is often associated with inherent porosity, especially near the surface and this is undesirable from the standpoint of structural integrity of the coating particularly for applications involving highly loaded parts. Laser-based postprocessing is an effective technique for eliminating these undesirable microstructural features without deteriorating the mechanical properties of the coating. In the present investigation, a low activity boronizing mixture was used for pack boriding of a medium carbon steel to obtain a single phase Fe2B layer. The coating was laser treated with a pulsed Nd–yttrium–aluminum–garnet laser at different laser powers to control the extent of melting of the boride layer. Characterization of both as-borided and laser treated coatings was carried out to examine changes in surface roughness, microstructural features, and microhardness profile and phases as a result of laser treatment. Testing of the coating under erosive and abrasive wear conditions was also carried out to ascertain the influence of laser treatment on tribological performance of the coating. It was found that, under controlled processing parameters, it is possible to improve the durability of coating properties through laser treatment.

Formation of hard tungsten boride layer by spark plasma sintering boriding

Metal borides are attractive candidates for high-temperature, wear resistance, and corrosion resistance applications. Tungsten borides (WB and W2B5) are known to have high hardness values, chemical inertness, and electronic conductivity, and have potential industrial applications as abrasive, corrosion-resistant and electrode materials, which are exposed to exacting environments. In this work, boride layers are formed on the surface of W samples using a pack boriding method with the assistant of the spark plasma sintering technique. The process was performed in the temperature range 1000–1400 °C with a holding time of 30 min. The microstructure, microhardness, and fracture toughness of the tungsten boride layer are investigated by optical microscopy, X-ray diffraction and microhardness indentations. Results showed that the boride layer, composed of WB, have thickness in the range ∼35–112 μm. The WB layers are found to have a preferred orientation in the (200) direction, which is reflected by a distinct columnar growth observed in the optical micrographs of polished cross-sections of SPS samples.

Characterization of the operative mechanism in potassium fluoborate activated pack boriding of steels

A mechanism that describes potassium fluoborate activated pack boriding of steels is proposed and validated with thermodynamic and empirical evidence. The process occurs via three distinct steps: release of boron trifluoride gas from the potassium fluoborate activator, formation of a thin layer of iron boride on the steel's surface accompanied by the release of carbon tetrafluoride and graphite, and finally, growth of the iron boride layer by direct reaction of iron with boron carbide. The presence of oxygen in the system inhibits the boriding process by converting the potassium fluoborate into oxygenyl boron fluoride prior to the release of boron trifluoride gas. In addition to characterizing the underlying mechanism for forming iron boride, the role of each of the ingredients of the potassium fluoborate pack is defined and the factors that determine the stoichiometry of the resultant boride layer are identified.

Boriding of mild steel using the spark plasma sintering (SPS) technique

The spark plasma sintering (SPS) technique was employed to perform boriding of mild steel. A pack boriding method that contained a silicon carbide–boron carbide powder pack mixture was utilized in this study. The process was performed in the temperature range 700–1000 °C for 30 min. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) revealed the microstructure and phase composition of the iron boride layers (FeB and Fe 2B). Plotting ln D vs. 1/ T expresses concisely the boride layer's growth rate constant ( D) vs. temperature ( T) relation. A linear relationship between ln D and 1/ T is confirmed. The kinetics of SPS boronization are discussed, and the effect of SPS on boronization is studied. The results confirmed that SPS required significantly lower activation energy for accomplishing the boriding operation.

Effect of borate coating on oxidation resistance of γ-TiAl intermetallic compound

Abstract The pack boriding process has been used to treat γ-TiAl intermetallic compound at a boriding temperature of 940°C for a boriding time of 8 h. A dense and continuous borided layer ca. 15 μm thick was obtained on γ-TiAl. The X-ray diffraction pattern depicts a single borate phase 9(A1,Ti) 2 O 3 B 2 O 3 formed in the borided layer. Cyclic oxidation behavior of the borate coating has been investigated at an oxidation temperature of 800°C with a total exposure time up to 100 h in air. The mass gain of the borate coating was 1.6 mg cm −2 , which is about three times lower than that of unborided γ-TiAl. The 9(Al,Ti) 2 O 3 B 2 O 3 phase decomposes slowly during the oxidation process at 800°C in air. The stable borate coating improves the high temperature oxidation resistance of γ-TiAl.

Evaluation of halide-activated pack boriding of INCONEL 722

Evaluation of halide-activated pack boriding of INCONEL 722

Plasmaborieren in einer BCl3-H2-Ar-Atmosphäre

The characterization of the BCl 3 -H 2 -Ar-glow discharge using the optical emission spectroscopy is a powerful method to suppress corrosive reactions at the substrate surface during plasma boriding, leading to non-porous boride layers. Wear tests on plasma-borided components show the same wear resistance as boride layers produced by the powder pack boriding method. These results make a significant contribution for getting an industrial realization of the plasma-assisted boriding technology.

Three-body abrasion of surface engineered die steel at elevated temperatures

Surface engineering techniques are being considered in the hot forging industry, for improving the life of forging dies. During forging, the surfaces of the dies reach temperatures of 700–800 °C. Published information on the wear performance of modified/engineered surfaces at higher temperatures is, however, scarce. To address this situation, a high-temperature pin-on-disc machine was modified into a ring-on-disc arrangement to facilitate the introduction of abrasive particles into the system, so that three-body abrasion tests could be conducted. In this paper, the results obtained from this machine on various modified surfaces at temperatures up to 600 °C in air using alumina abrasive particles are presented and discussed. The surface treatments studied include hardfacing with Satellite 6, pack boriding, gas nitriding and nitrocarburising. For some treatments, the test results indicated a decrease in wear rate with increasing temperature, but for others there was no change with temperature. The wear track on the siscs were examined by light microscopy and scanning electron microscopy (with energy dispersive X-ray spectroscopy) to determine the wear mechanisms of the modified surfaces. Microcutting is believed to be one of the mechanisms occurring in these tests. The hot strength of the surface layer, however, determines the performance at higher temperatures. The importance of surface oxidation and of abrasive embedment in the surface, in determining the abrasive wear rates, is also discussed.