Maciej Jan Kupczyk

Evaluation of Cutting Edges Made of Nanocrystalline Cemented Carbides Sintered by the Pulse Plasma Method

In our investigations, nanocrystalline WC-5 wt % Co was consolidated by the pulse plasma sintering method at various temperatures between 1320 and 1560 K under a pressure of 60 MPa for 300 s. The cemented carbides sintered at 1520 K have a relative density of 100 %, hardness of 2100 HV30, and tungsten carbides WC crystallite size of about 150-300 nm. An increase of the sintering temperature to 1560 K results in the increase of the WC crystallite size to about 300-500 nm and the hardness being decreased to 1980 HV30. The tool life of the cutting edges made of nanocrystalline cemented carbides sintered by the pulse plasma method is increased about two times in comparison with cutting edges made of standard and fine-grained cemented carbides during the turning of EN1.45.40 1H18N9T austenitic steel. On the basis of the literature data 1-4 and our own investigations 5-8, a decrease reduction of the tungsten carbides WC grain size in WC-Co cemented carbides increases the fracture toughness, bending strength, and hardness. WC-Co cemented carbides are most often produced by sintering with the partici- pation of a liquid cobalt phase. The presence of a liquid cobalt phase during the WC-Co sintering causes the growth of the WC grains. The growth of the WC grains is due to the high rate of diffusion of WC through the liquid cobalt phase. In the newest sintering methods; for example, spark plasma sintering SPS, field assisted sintering FAST, and plasma assisted sintering PAS9-11, the sintering process is very short and carried out at a lower temperature than in the conventional methods. A characteristic feature of the SPS, FAST, and PAS methods is a current pulse for heating the powders during sintering. Spark discharges during a current pulse are ignited in the pores. The discharges formed in the pores remove absorbed gases and oxides from the surface of powder particles, thereby facilitating the formation of active contact between them. The present investigation was concerned with sintering nanocrystalline WC-5 wt % Co powders using a new pulse plasma sintering PPS method 12. As in the SPS, PAS, and FAST methods, in the PPS method the spark discharges during a current pulse are ignited in the pores. The phenomena occurring in the PPS process are shown in Fig. 1. In this article, the results of a comparative investigation of the durability of cutting edges made of nanocrystalline WC-5 wt % Co cemented carbides sintered by the pulse plasma method and cutting edges made of standard and fine-grained cemented carbides 1.5 m of the same chemical composition during the turning of EN1.45.40 1H18N9T austenitic steel are presented. Austenitic steel, widely applied in the food and chemical industry, belongs to hard machinable materials 13. The hard machinability of auste- nitic steel comes from a surface hardening phenomenon during machining. Therefore, the machining is carried out with very low cutting parameters. For this reason, the investigations of nanocrystalline ce- mented carbides were taken into consideration. The nanocrystalline cemented carbides are significantly harder and more wear resistant then the standard or fine-grained cemented carbides 4-6.

Influence of Structure on Brittleness of Boron Nitride Coatings Deposited on Cemented Fine-Grained Carbides

The article presents the brittleness study of boron nitride coatings deposited on cutting edges made of fine-grained cemented carbides by the pulse-plasma method (PPD). Influences of the structure (density, pores, microcracks) of coating material on the brittleness and on selected technological parameters of boron nitride formation by PPD method particularly taking into account discharge voltage on brittleness are shown. Differences between values of total average crack length ΣL, critical loads (Pk300, Pk500), and coefficients (a1(300) and a1(500)) characterized susceptibility to cracking of investigated coatings manufactured using different values of production process were defined. Results of investigations have confirmed the usefulness of Palmqvist’s method for measurement of coating susceptibility to brittle cracking.

Application of Cutting Edges with High Durability Made of Nanocrystalline Cemented Carbides

This chapter presents the results of the wear and durability investigations of cutting insert edges made of Nano_WC-5Co and Nano_WC-5Co + Cr3C2 nanocrystalline sintered carbides. Cutting inserts were sintered using nanocrystalline powder by the pulse-plasma method. Durability of the cutting edges was determined during turning of EN 1.45.41 (1H18N9T) austenitic steel. The Nano_WC-5Co + 0.9% Cr3C2 nanocrystalline cemented carbides have much higher hardness and smaller average grain size than the Nano_WC-5Co nanocrystalline carbides without growth inhibitor. For these reasons, cutting inserts made of the nanocrystalline cemented carbides with 0.9% Cr3C2 by weight exhibited significantly greater resistance to wear and greater durability during machining of austenitic steel.

Design of Nanocrystalline Cemented Carbides with High Hardness

This chapter presents results concerning the influence of the sintering parameters on the hardness and structure of the Nano_WC-5Co nanocrystalline cemented carbides with Cr3C2 (0.3, 0.6 and 0.9%) growth inhibitor and without it. The cutting edges made of nanocrystalline cemented carbides were sintered using the Pulse Plasma Sintering (PPS) method. During the manufacturing process of cutting inserts, various values of both sintering temperature and sintering time were applied. Due to the pulse character of the PPS method and the phenomena accompanying the pulse process, pulse sintering allows for more efficient production of sintered tool material than conventional methods.

Porównanie właściwości ostrzy skrawających ze stali szybkotnących wytworzonych metodami konwencjonalnymi i w procesie metalurgii proszków

Selected fragments of investigations of technological and functional properties of cutting edges made of conventional and sintered high speed steel with similar chemical composition are presented. Investigations of technological and functional properties have comparative character and concern among other things estimation of chemical composition, hardness, structure and durability during toughening steel machining.