Surface treatment of sintered hard alloys with a highly concentrated plasma jet

Самотугин, С. С.; Koval’chuk, A. V.; Ovchinńikov, V. M.

doi:10.1080/09507119409548702

Cited by 4 publications

(10 citation statements)

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“…1 ' 2 The wear resistance of the cutting edge greatly increases as a result of the formation of a zone with a disperse structure and high hardness. However, as shown by practice, ~ 30-50% of tools (especially hardalloy tools) fail as a result of brittle fracture and chipping.…”

Section: Priazovsk State Technical Universitymentioning

confidence: 99%

“…Using a general solution of the axisymmetric problem for a disc crack in an infinite medium with tensile stresses at the edges of the crack, it was possible to derive correct relationships linking the critical stress concentration factor K lc of the material of the specimen with the critical load for the stage of crack nucleation F c and crack length 1 for the stage of its propagation: [1] Orc) 3/2 tan where c = a + 1 (see Fig. 1, 2a -diagonal of the indentation); 2/?…”

Section: Priazovsk State Technical Universitymentioning

confidence: 99%

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Structure and cracking resistance of hard alloys in plasma treatment

Самотугин¹,

Novokhatskaya²

1996

Welding International

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Surface treatment with a high-concentration plasma jet is a promising method of improving the service characteristics of tool materials. 1 ' 2 The wear resistance of the cutting edge greatly increases as a result of the formation of a zone with a disperse structure and high hardness. However, as shown by practice, ~ 30-50% of tools (especially hardalloy tools) fail as a result of brittle fracture and chipping. Microcracks, formed at the cutting edge under the effect of normal tensile and tangential stresses, increase the degree of wear, thus greatly increasing the cutting force and, consequently, the probability of fracture. Therefore, when developing new tool materials or methods of hardening them, it is very important, in addition to analysing the conventional criteria of efficiency (hardness, heat resistance), to use the criteria of short-term strength cracking resistance on the basis of the brittle fracture mechanism.As regards the steel tools, the effect of surface hardening on dynamic cracking resistance (critical stress concentration factor K°, impact toughness KC and its component) can be evaluated in impact tests on specimens of standard dimensions with a special notch using the dynamic fracture diagram. 2 For sintered hard alloys these tests in practice are highly complicated, because of both the problems in producing specimens and the consumption of a large amount of material. It is therefore promising to use the microtests to determine cracking resistance under local loading. For hard and brittle materials, local plane strain with the formation of a half-disc crack occurs during indentation into the surface of the specimen of an indentor made of a harder material, such as a Vickers diamond pyramid (Fig. 1).Using a general solution of the axisymmetric problem for a disc crack in an infinite medium with tensile stresses at the edges of the crack, it was possible to derive correct 2 Diagram showing position of the hardened zone on hard-alloy sheets of triangular (a) and square (b) shape.relationships linking the critical stress concentration factor K lc of the material of the specimen with the critical load for the stage of crack nucleation F c and crack length 1 for the stage of its propagation: [1] Orc) 3/2 tan 1 Diagram of formation of cracks under local loading with a Vickers pyramid.where c = a + 1 (see Fig. 1, 2a -diagonal of the indentation); 2/? = 136° -angle between the opposite edges of the Vickers pyramid.This method is simple and universal. Tests were carried out simultaneously and HV hardness is measured by standard hardness meters. The effect of surface treatment can be evaluated on one specimen by consecutive loading in the hardened zone and initial metal. The correlation of the resultant values of K lc with the values determined by conventional methods was determined for a wide range of hard and brittle materials, including tool hard alloys. This method can also be used for steel specimens with hard and brittle surface coatings, for example in depositing carbides or borides and in nitridi...

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Section: Priazovsk State Technical Universitymentioning

confidence: 99%

Section: Priazovsk State Technical Universitymentioning

confidence: 99%

Structure and cracking resistance of hard alloys in plasma treatment

Самотугин¹,

Novokhatskaya²

1996

Welding International

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“…6,7 Remelting of boron coatings with this technique was used to enhance their wear and corrosion performance. [8][9][10] PTA has also been used as a heat source in order to alloy cast irons, plain steels and tool steels by melting their surface covered with various powders in order to produce hard and wear resistant coatings.…”

Section: Introductionmentioning

confidence: 99%

Study of the operational parameters of plasma transferred arc melting and modelling of the process

Bourithis¹,

Papadimitriou²

2005

Science and Technology of Welding and Joining

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Plasma transferred arc (PTA) melting/alloying technique can be successfully used in various surface modification applications and has the potential for industrial use, replacing other more expensive techniques such as laser or electron beam. Such applications require tight control of the process parameters. There is a restricted field of PTA parameter values, where PTA melting can be successfully performed with smooth and unoxidised surfaces. The heat source efficiency of PTA treatment is strongly affected by welding current, arc length and travel speed of the arc and it takes values between 0 . 40 and 0 . 55, while melting efficiency takes values between 0 . 05 and 0 . 25, affected by the same parameters as arc efficiency. The microstructure and hardness of the melting zone of a PTA pass is associated with heat input and arc length.

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“…This treatment variant is effective for high-speed steels 14 and, in particular, sintered hard alloys. 3 In the examined range of variation of the conditions of plasma micromelting R6M5 steel, it was not possible to obtain a structure of the cast zone with an equiaxed dendritic-cellular appearance ensuring, in laser melting, the highest hardness values. 1 At the same time, crystallisation cracks, a significant defect of laser melting tool steels, 7 ' 13 were not detected in plasma micromelting.…”

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confidence: 97%

“…3 ' 4 Of these methods, the latter has the most suitable economic parameters and productivity because of its low cost, availability of equipment and a large hardened zone. It has been shown efficient to use plasma processing to harden tools made of high-speed steels, 4 sintered hard alloys, 3 and carbon and low-alloy tool steels. 5 At present, laser and electron beam hardening of tools is carried out in the majority of cases with surface melting, whereas plasma hardening is carried out without melting by phase and structural transformations in the solid state and as a result of the differences in the nature of the effect of highly concentrated sources on the metal surface.…”

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confidence: 99%