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Hardness prediction of a cold rolled Nimonic 80A exhaust valve spindle

Kang S. W., Heo S. J., Yoo J. H., Kang J. H.

Journal of Achievements in Materials and Manufacturing Engineering

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2019

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Vol. 94, nr 1-2

13--21

EN

Purpose: of this paper is to predict the hardness of cold rolled exhausts valve spindle fabricated of Nimonic 80A via axisymmetric finite element analysis, compression testing, and hardness inspection. Design/methodology/approach: The stress-strain relationship of Nimonic 80A was obtained via compression testing with deformation ratios of 10%, 20%, and 30%. Hardness changes caused by the strain hardening effect were measured in cut specimens in both the axial and circumferential directions following compression testing. The effective strain at the measurement position was calculated via finite element analysis. The regression equation for hardness changes caused by work hardening was derived from analysed strain and inspected hardness. The cold-rolling deformation of an exhaust valve spindle was analysed using axisymmetric finite element analysis. Findings: The stress-strain relationship calculated from compression testing was well expressed using the Holloman equation and the strain-hardness relationship by strain hardening was successfully regressed using the shifted power law model for Nimonic 80A, Nickel-Chromium based super alloy. Research limitations/implications: This research focused hardness prediction of spindle after ring rolling operation for generating beneficial compressive surface residual stresses for enhancing fatigue life. Further research to quantify compressive residual stress after rolling shall be followed to increase fatigue life. Practical implications: The cold rolling process is a typical incremental forming method and should be analysed under three-dimensional conditions. However, it takes lots of time to solve incremental forming analysis. To predict hardness distribution after rolling in the manufacturing field, FE analysis was performed under two-dimensional axisymmetric conditions based on the assumption of no friction generated by the rolling tool. The deformed shapes and hardness distribution from the inspection quality standard and two-dimensional FE analysis showed very similar results. Simplified finite element analysis method for ring rolling process for local area could be very effective method in the industrial field. Originality/value: The stress-strain relationship and the hardness and strain relationship were derived by compression test and hardness measurement for compressed specimen for Nimonic 80A, Nickel-Chromium based super alloy. And simplified finite element analysis method was suggested to predict deformed shape and hardness distribution of locally cold rolled region and achieved similar result between FE analysis result and Quality standard. Suggested method would be very effective method to engine spindle manufacture to predict hardness of different size of product.

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Fracture toughness of gas borided Nimonic 80A alloy

Makuch N., Kulka M., Dziarski P.

Inżynieria Materiałowa

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2016

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Vol. 37, nr 1

10--15

EN

Ni-based superalloys are often used in many industrial applications, for example in chemical, petrochemical, aeronautics, nuclear or space industries. These alloys are characterized by a unique combination of low thermal expansion coefficient, high temperature strength, high resistance to oxidation and high corrosion resistance. However, due to their low microhardness and sensitivity to abrasive, erosive and adhesive wear, their application is limited. The boriding process is the appropriate treatment, which will provide high hardness and high wear resistance of Ni-based alloys. Unfortunately, the use of boride layers is limited by their sensibility to cracking under mechanical stresses. Therefore, in this paper the microstructure, microhardness and fracture toughness of gas-borided layer produced on Nimonic 80A alloy were studied. Gas boriding in N2–H2–BCl3 atmosphere was proposed to produce the hard boride layer on Nimonic 80A alloy. This process was carried out at 920°C (1193 K) for 2 hours. The carrier gas consisted of 75 vol.% N2 and 25 vol.% H2. Proposed gas boriding accelerated the diffusion of boron into the surface in comparison with other acceptable diffusion methods. The comparable thickness of boride layer was obtained after considerably shorter duration.

PL

Stopy na bazie Ni są często stosowane w przemyśle ze względu na unikatowe połączenie właściwości: dużej żarowytrzymałości, dobrej odporności na utlenianie i korozję. Jednakże ze względu na ich małą twardość i wrażliwość na zużycie przez tarcie ich zastosowanie jest ograniczone. Proces borowania jest obróbką zapewniającą dużą twardość i odporność na zużycie stopów na bazie Ni. Niestety, zastosowanie warstw borowanych jest ograniczone z powodu ich wrażliwości na pękanie. Celem pracy było określenie odporności na kruche pękanie warstw borowanych gazowo wytworzonych na stopie Nimonic 80A. Ze względu na skład fazowy tych warstw (borki niklu i borki chromu) pomiary odporności na kruche pękanie przeprowadzono na prostopadłym przekroju warstwy, w różnych odległościach od powierzchni. Ponadto przeprowadzono badania mikrostruktury i wyznaczono profil mikrotwardości.

3

Gas boriding of Nimonic 80A alloy

Makuch N., Kulka M., Dziarski P.

Inżynieria Materiałowa

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2015

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Vol. 36, nr 3

124--128

EN

The excellent resistance of Ni-based alloys to corrosion and oxidation has led them being used wherever corrosive media or high temperature are to be expected. However, if Ni-based alloys have to be applied under conditions of appreciable mechanical wear (adhesive or abrasive), these materials require suitable wear protection. Gas boriding in N2–H2–BCl3 atmosphere was proposed to formation of boride layers on Nimonic 80A alloy. This process was carried out at 920°C (1193 K) for 3 hours. The carrier gas consisted of 75 vol. % N2 and 25 vol. % H2. The gases of high purity were used (nitrogen 6.0 and hydrogen 6.0). BCl3 addition was equal to about 1.3 vol. % in relation to the entire atmosphere used (N2–H2–BCl3). The microstructure and some properties of produced layer were studied. Proposed gas boriding accelerated the diffusion of boron into the surface in comparison with other acceptable diffusion methods. The comparable thickness of boride layer was obtained after considerably shorter duration. The significant improvement of hardness was observed as a consequence of gas boriding.

PL

Bardzo dobra odporność stopów niklu na korozję i utlenianie pozwala stosować je tam, gdzie występuje agresywne środowisko lub wysoka temperatura. Jednak stosowanie tych stopów w warunkach znacznego zużycia mechanicznego (adhezyjnego lub ściernego) wymaga odpowiedniego zabezpieczenia. Zaproponowano borowanie gazowe w atmosferze N2–H2–BCl3 do wytworzenia warstwy borków na stopie Nimonic 80A. Proces prowadzono w temperaturze 920°C (1193 K) przez 3 godziny. Gaz nośny zawierał 75% N2 i 25% H2. Stosowano gazy o dużej czystości (azot 6.0 i wodór 6.0). Dodatek BCl3 wynosił około 1,3% w odniesieniu do całej stosowanej atmosfery (N2–H2–BCl3). Podczas pierwszego etapu procesu do atmosfery N2–H2 dodawano BCl3. Badano mikrostrukturę i niektóre właściwości warstwy borowanej. Proponowane borowanie gazowe powodowało przyspieszenie dyfuzji boru do powierzchni w porównaniu z innymi metodami dyfuzyjnymi. Otrzymano porównywalną grubość warstwy borków po znacznie krótszym czasie trwania procesu. Mikroanaliza rentgenowska wykazała zwiększone stężenie boru w warstwie. Zaobserwowano znaczne zwiększenie twardości w wyniku gazowego borowania.