Student Number : 0413336G - MSc(Eng)dissertation - School of Chemical and Metallurgical Engineering - Faculty of Engineering and the Built Environment / This dissertation reports systematic work aimed at determining the plastic deformation mechanisms that led to strains at fracture as high as 4.7% in WC-Co alloys at 1000°C when subjected to 3-point bending tests. The three grades investigated have a Co content of 15wt% and WC grain sizes of 1.3, 0.35 and 0.3 μ m respectively and were received after they were tested in bending. Fractography, macrostructural and microstructural investigations were carried out in attempts to identify the mechanisms leading to the large strains. Techniques used included light microscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and quantitative image analysis. Through comparisons of the results from the three grades at various temperatures, it was possible to establish that the large strain at 1000°C are mainly due to cracking and cobalt drift. During the fractographic investigations it was found that the grades which contained VC as a grain refiner exhibited steps on the WC grains and that fracture propagated preferentially along the stepped WC grain boundaries.

The growth of TiN on cemented carbide, deposited by chemical vapour deposition (CVD), was studied. Today TiN is used as a seeding layer between the cemented carbide and the following layer. Previous experiments have shown that the coverage is uneven on the cemented carbide surface showing pits with a different growth than the main part of the surface. These pits most likely occur on some of the WC surfaces. Therefore the growth and orientation relation between the two phases were examined. Cemented carbide specimens were deposited with TiN under two different pressures and with different deposition time to give a layer as thick as the seeding layer used in the production and one about ten times thicker to study growth after the whole surface had been covered. Two pre-treatments where used on the specimens; one which were polishing with diamond and the other where the specimens were boiled in acid to remove the binder phase and expose the WC surfaces. The specimens were studied using XRD and a SEM equipped with EDS and EBSD detectors. The pictures taken with SEM showed that initial growth occurred at grain boundaries and polishing scratches. It also showed that growth occurred on all surfaces, which were confirmed by EDS. Both processes showed about the same appearance in the thinner layers but very different appearance in the thicker. This was confirmed by XRD were the thinner layers showed about the same result while the thicker ones differ from one another. Thus further growth is dependent on the parameters of the CVD process and not the surface beneath. EBSD showed an orientation relation between TiN and WC crystals in both processes. The process at lower pressure gave much finer grains which were difficult to index with EBSD, giving results in only three points. The process at higher pressure gave coarser grains which were more easily indexed. The relations WC{0001}-TiN{110}, giving WC{101̅0}-TiN{100}, and WC{0001}-TiN{111}, giving WC{101̅0}-TiN{211}, could be seen in more than one point. These results are consistent with previous studies of the growth of TiC on WC. This comparison between TiC and TiN makes it possible to draw the conclusion that also Ti(C,N) should behave the same. It also shows an orientation relation that is consistent no matter what WC plane is on the surface. The poor growth and the pits depend on the growth orientation of TiN on each specific WC surface.

Steel turning inserts cemented carbides have a binder phase consisting of cobalt (Co). However, in recent years a study from the United States National Toxicity Program (NTP) found that cobalt powder is carcinogenic upon inhalation. The European Union's REACH have therefore also classified cobalt powder as carcinogenic upon inhalation. The worldwide search to find a replacement has therefore lately intensified. It is important that the alternative binder phase has no negative effects on the properties of the insert. In this thesis the adhesion between a multilayer ceramic chemical vapor deposition (CVD) coating and a cemented carbide with the alternative binder phases consisting of iron (Fe), nickel (Ni) and cobalt (Co) has been studied. First of all, the fracture surfaces showed that the CVD coating was able to grow on all cemented carbides, regardless of which binder phase. To evaluate the adhesion, scratch tests were performed on all samples. The results from the scratch tests were not as expected. No chipping of the coating down to the cemented carbide occurred on any of the samples and the samples with the hardest cemented carbide did not get the highest critical load, which it should according to the literature if all other parameters were the same. Instead the sample with the binder phase consisting of 73 wt% iron and 27 wt% nickel had the highest critical load. This is thought to be due to that during the scratch test the binder phase in this cemented carbide would most likely transform into deformation martensite.

Pressing of metallic powders is a manufacturing process widely investigated in the research field and in the industry. This thesis project is focused on optimizing the pressing process of cemented carbide powder utilized for the production of triangular shaped cutting tool inserts. In particular, the filling of powder into the die cavity was investigated with respect to different pressing parameters. The aim of the project was to obtain a uniform density distribution of the powder into the die cavity, and hence to reduce the variation of the height of the insert obtaining more precise dimension of the latter. The tests were carried out at the Sandvik Coromant production department which is the creator of the project. The optimization of the pressing process was performed according to the Design of experiments theory. The dynamic of the sintering process was also investigated. The results showed a significant improvement in the filling of the die cavity and a significant decrease of the variation of the height of the inserts. The new insert obtained has more precise dimensions and is able to meet the more demanding requirements of the customers. The results achieved are directly applicable to a larger number of products, and indicate the direction to follow for further development of the manufacturing process.

The aim of this master thesis was to compare EELS in TEM with TEM-EDS and WDS-EPMA for quantitative analysis of γ-phase in cemented carbide. Especially, the quantification of the light elements nitrogen and carbon in compounds like TiCxN1-x is interesting, since this is problematic. The techniques were compared by acquiring spectra for quantification of two samples of cemented carbide containing γ-phase (Tix,W1-x)(CyN1-y) with different nitrogen and tungsten content. Also, a rigorous evaluation about how EELS spectra best is acquired and processed was performed in order to enable the comparison. Experimental results show that EELS gives satisfying results for TiC0.7N0.3 and that EELS is comparable with WDS-EPMA for quantification of nitrogen, carbon and titanium in (Tix,W1-x)(CyN1-y) when the atomic concentration of nitrogen is around 20%. However, EELS was not used for quantification of tungsten. Concluded is also that EELS and WDS should be considered as complementary rather than competing techniques.

This thesis work sought to find a tribological testing method suitable for cementedcarbide drill bit inserts used when drilling rock. A review of the literature publishedon the matter showed that there are quite a few test methods developed for wearstudies with cemented carbides, but most of them were not designed for the rockdrilling industry. Published studies performed with the found methods and articleswith analyzed field tests have been studied. It is generally agreed upon that the stepsof wear is that the binder disappears first, followed by removal of carbide grains. Themechanisms of binder phase and carbide grain removal is somewhat debated, butalmost every study observes fracture of the carbide grains. The wear test created inthis thesis was shown to give wear linear with time, but not with load. The newmethod was shown to be capable of distinguishing between different cementedcarbides worn in three body abrasion against different rocks. Analysis of the wornsamples shows that there are similarities with bit inserts worn in field testing. Many ofthe observations made during the analysis are also similar to observations inliterature.

This thesis work is performed at Sandvik Mining Rock Tools, a world leading supplier of rock drilling tools. The work is part of developing a new tribological wear test method for cemented carbide drill bit inserts. The test method has earlier been judged successful in mimicking the rotary-percussive rock drilling process because it gives the same wear mechanisms as have been observed for inserts used in rock drilling. During testing the cemented carbide drill bit insert is pressed against a moving rock surface while water and particles are added to the contact area. The particles are present to simulate the rock crushings formed during drilling. They are believed to cause abrasive wear of the inserts. In this work the effect of load, particle material and particle size are studied. When adding silica particles, which are softer than the cemented carbide material, no correlation is obtained between wear rate and load or particle size. Cracking of WC grains, added rock material and removal of pieces of carbide material are seen at the worn sample surfaces. These observations are similar to observations described in other works about wear of cemented carbide. Adding alumina particles, which are harder than the sample material, gives high wear rate and ground/striped sample surfaces. The wear rate increases with alumina particle size.

An experimental ball-milling study was performed to compare the deagglomeration behavior and the evolution of the particle size distribution with increasing milling time of two relatively coarse WC powders used for the production of cemented carbide cutting tools. The WC-powders were found to have distinctly different particle size distributions and particle morphologies prior to milling. Lab-scale WC samples were made using a range of different process parameters and milling times. These were then analysed by means of microscopy, laser light scattering, gas adsorption BET analysis and X-ray powder diffraction, XRD, to attain particle size distribution, specific surface area and a mean crystal size, respectively. The results suggested a linear relation between log(particle size) and log(milling time) between 10 and 80 hours milling. The viscosity was shown to have a minor effect on the milling efficiency. Both the number of collisions of milling balls per unit time as well as the kinetic energy of the milling ball affected the size reduction; more collisions or higher energy resulted in a higher milling efficiency. The evaluation of the effect of the process parameters on milling efficiency was facilitated by the use of simple scaling factors. For example, all milling curves for samples with different WC amounts coincided when rescaling the milling time using a scaling factor based on the weight of the WC and milling balls. The same scaling factor could be used with success for rescaling the results from different trials obtained with laser light scattering, gas adsorption and XRD. The results of this work are useful for future work on modeling of the milling process which should lead to more accurate predictions of the outcome of milling unit operations.

In today’s inserts used for metal cutting the binder phase consists of cobalt (Co).However, EU’s REACH programme and the U.S’s National Toxicity Programme(NTP) classified Co as toxic/carcinogenic. Therefore, there is a strong need toinvestigate alternative binder phases. This thesis covers sintering and characterisationof cemented carbide with a binder phase consisting of nickel (Ni) and iron (Fe) withthe composition of 85Ni:15Fe. The aim was to study the gradient formation of turninginsert and find sintering processes to achieve a gradient structure with the targetedthickness of 26 microns. Simulations in ThermoCalc provided a suitable composition and a starting point forsintering parameters. The influences of sintering process parameters, such as holdingtime, temperature and counter pressure on the formation of the gradient zone wereinvestigated. Hot isostatic pressing (HIP) sintering was done in order to study thegradient formation as well as to reduce the porosity when needed. Sintered insertswere analysed by light optical microscopy. It was found that there are at least three possible ways to control the formation ofthe gradient: sintering in vacuum with a holding time of 20 min at 1450°C, sintering at1450°C with a counter pressure of 5 mbar nitrogen, and sintering with a counterpressure of 11.5 mbar followed by a double sinter-hip with 55 bar argon atmosphere.However, only the last process fulfilled the microstructure criteria in terms ofporosity and binder phase distribution. It is clear that the formation of gradient zonesin 85Ni:15Fe can be predicted, however calculations and simulations need to beoptimized in order to get more accurate results.

The present work was conducted in Sandvik Coromant to enhance the knowledge and understanding of general flank wear growth and specifically in this case flank wear growth on the cutting edge of the coated (Ti(C, N)/ Al2O3/ TiN) tool inserts.   Reliable modeling of tool life is always a concern for machining processes. Numbers of wear models studies predicting the tool life length have been created throughout the metal-cutting history to better predict and thereby control the tool life span, which is a major portion of the total cost of machining.   A geometrical contact model defining the geometry of the flank wear growth on the cutting tool inserts was proposed and then compared with four suggested models, which estimates flank wear. The focus of this work is on the initial growth of flank wear process and thereby short cutting-time intervals are measured.   Wear tests on cutting tool inserts were performed after orthogonal turning of Ovako 825 B steel and were analysed by optical instrument, 3D optical imaging in Alicona InfiniteFocus and EDS in SEM. Force measurements for cutting speeds, Vc, 150, 200, and 250 m/min and feed rate, fn, 0.15 mm/rev were recorded as well.   Results show that initial flank wear land, VB, growth is dominated by sliding distance per cutting length for different cutting speeds. A good correlation between the geometrical contact model and estimation models is indentified. The cutting force measurements compared with the flank wear land show proportionality between two parameters. For the machining data in the present study the flank wear rate per sliding distance, dW/dL, is estimated to 2x103 (μ3/m).