Júlio César Giubilei Milan

Some observations on wear and damages in cemented carbide tools

Cutting tools are subjected to extremely unfavorable conditions during machining operations. High cutting temperatures, compressive and shearing stresses, chemical attacks, variable cyclic thermal and mechanical loads are some adverse conditions that wear and damage these tools. Therefore, it is crucial to understand the process of tool wear and damage and how the cutting parameters affect it in order to underpin decisions regarding the most favorable conditions to address the problem. This article treats on some forms and mechanism of wear and damage that cemented carbides can undergo during machining. Special attention was given to damages caused during interrupted cutting (e.g., milling), such as fracture, chipping and thermal fatigue. Experimental details and results of the latter phenomenon, which was studied under different cutting conditions, are discussed and confronted with literature. Keywords : Cemented carbide tools, milling, tool damage, thermal fatigue

Tribological behaviour of borided H13 steel with different boriding agents

Abstract Solid boriding thermochemical treatment was carried out on AISI H13 steel. Two boriding agents were used: Ekabor 1-V2 commercial powder and a mixture of 73·26 wt-% borax, 24·06 wt-%SiC, 1·22 wt-%NH4Cl and 1·46 wt-%NaCl. Pin on disc wear tests were carried out to investigate tribological behaviour. After the wear tests, samples were cut in cross-section to evaluate the thickness and morphology of the boride layer by scanning electron microscopy (SEM) and Vickers microhardness. Wear mechanisms were evaluated by SEM. A large improvement in wear resistance was observed for borided samples compared with samples that had been quenched and tempered. The thickness of the borided layer was higher for samples borided with Ekabor powder than those borided with the mixture. In comparison with quenched and tempered samples, borided samples had a higher incidence of cracks, which favours spalling and reduction of grooves formed by abrasive wear.

Acquired Properties Comparison of Solid Nitriding, Gas Nitriding and Plasma Nitriding in Tool Steels

Plasma nitriding, gas nitriding and solid nitriding were applied in tool steels (AISI H13, AISI P20 and N-8550). The acquired properties were compared and evaluated on these three processes with the aim to verify the solid nitriding performance. In order to promote the solid nitriding, the samples were surrounded by a solid compound with the Fe4KCN stoichiometric formula, inside an aluminum recipient. All thermochemical nitriding processes were performed at 560 °C. The wear behavior has been assessed by dry sliding wear test, using a pin-on-disk apparatus, the amount of wear was obtained by the use of a profilometer. The wear tracks were analyzed using SEM (Scanning Electron Microscopy). After the wear test the samples were transversally cut, to obtain the Vickers microhardness. Solid nitriding presented good performance, formation of a nitriding layer, values of microhardness compatible with the other processes and the best results of wear.

Nanocomposite of photocurable epoxy-acrylate resin and carbon nanotubes: dynamic-mechanical, thermal and tribological properties

In this study, the thermal, dynamic-mechanical and tribological behavior of nanocomposites of a photocurable epoxy-acrylate resin and multiwalled carbon nanotubes (MWCNT) are investigated. A route consisting of a combination of sonication, mechanical and magnetic stirring is used to disperse 0.25-0.75 wt. (%) MWCNT into the resin. Two photocuring cycles using 12 hours and 24 hours of UV-A radiation are studied. The storage modulus, the loss modulus and the tan delta are obtained by dynamic mechanical analysis. Thermal stability is investigated by thermogravimetry, morphology by transmission electronic microscopy (TEM) and tribological performance using a pin-on-disk apparatus. The results indicate an increase in stiffness and higher ability to dissipate energy, as well as a shift in the glass transition temperature for the nanocomposites. The addition of nanofillers also decreased friction coefficient and wear rate of the nanocomposites but did not change the observed wear mechanisms.

Study of the nitrided layer obtained by different nitriding methods

In this study, plasma nitriding, gas nitriding and solid nitriding were performed in AISI H13, AISI P20 and N-8550 tool steels. The aim of the study was compare the acquired properties after the thermochemical treatments and evaluate the efficiency of the solid nitriding treatment. The samples were analyzed using a microhardness tester and a scanning electron microscope. The typical nitriding layers were observed - white layer and diffusion layer. The phases Fe4N - γ´ and Fe2,3N - e were identified using an X- Ray diffractometer. The microhardness values of the nitrided layers obtained by the solid nitriding treatment were compatible with the other values of microhardness obtained by plasma and gas nitriding. The thickness of the nitrided layer obtained by the solid nitriding treatment was irregular.

Propriedades mecânicas, tribológicas e térmicas de nanocompósitos de PLLA com nanotubos de carbono de paredes múltiplas

This work studied the effects of the addition of Multiwalled Carbon Nanotubes (MWCNT) to a PLLA matrix. Two distinct methods of preparation were employed: a combination of a solvent/ mechanical stirring and a combination of a solvent/high energy sonication. The mechanical properties of the nanocomposites were determined by nanoindentation and by the Vickers hardness test. Thermal properties of the nanocomposites (Tg, Tc, Tm and crystallinity degree) were determined by DSC. The tribological properties of the nanocomposites were determined by using a pin-on-disc apparatus. Mechanical and thermal properties did not present significant alterations, although tribological properties presented significant changes caused by the method of preparation and different loads. SEM images indicated that the wear mechanism was changed by the addition of MWCNT.

Influence of cutting tool geometry, feed rate and cutting fluid on the machinability of Inconel 751

Inconel represents a family of nickel-based super alloys with a wide range of application including components that work at high temperatures. Despite of this, nickel-based super alloys are generally known to be one of the most difficult materials to machine. In this paper, attention is focused on the machinability of Inconel 751 which is a nickel-based super alloy normally used to manufacture exhaust valves of internal-combustion engines. In this case, an experimental investigation where a series of dry and wet rapid facing trials (turning) using coated carbide tools were performed. Metal removing process was carried out for two different feed rates and two different tool geometries. For indirectly quantifying the tool wear, the machined surface profile has been measured using a centesimal dial gauge. Moreover, cutting tools have been analysed with a scanning electronic microscope. The results provide important practical information about the machinability of Inconel 751.