Chemical interactions that drive crater wear in turning are often studied using diffusion couples where the tool and workpiece are fixed. In contrast, in actual turning, there is a constant supply of new workpiece material at the tool-chip interface. In this work, diffusion simulations of a WC-Co(6%) and Ti-5Al-5V system were conducted, with constant replenishment of titanium at the interface (open system) and a fixed amount of material (closed system). The simulations showed that the formation of W(bcc), ry-phase, and TiC is dependent on the activity of C and the permeability of Co and C in titanium. Scanning and transmission electron microscopy-based techniques were used to analyse a Ti-5Al-5V-5Mo-3Cr and WC-Co(6%) diffusion couple and a worn WC-Co(6%) insert. The sequence of phases in the closed system simulation was similar to that observed in the diffusion couple. The open system simulation indicated that W(bcc) can form at WC-WC boundaries (where Co is low) within the subsurface of a WC-Co(6%) that has adhered titanium, and at the WC/Ti interface. Additionally, high densities of stacking faults and dislocations were found within subsurface WC grains, indicating a significant reduction of the tool's integrity.

Liquid phase migration (LPM) and its potential impact on the phenomenon known as cobalt capping in cemented carbides have been investigated through experiments on fully densified, pre-sintered samples and simulations. A model for LPM was developed based on interface energies, grain size, and contiguity, and was implemented and integrated with Thermo-Calc software to make predictions about the final microstructure. The model's predictions, when applied to cases with gradients in grain size and volume fraction of the binder phase, were found to somewhat match experimental observations. Additionally, it was obsereved that LPM can cause a phenomenon resembling cobalt capping due to gradients in carbon activity.

Conventional cemented carbide is recommended for machining Ti6Al4V. However, polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (pcBN) also show promise. Demands for higher productivity accelerate diffusional dissolution and chemically driven wear mechanisms in these tool materials. This study investigates active wear mechanisms by studying the interactions between Ti6Al4V and PCD, pcBN, and cemented carbide tools in diffusion couples at temperatures from 900° to 1300°C. All tool materials suffered from diffusion to varying degrees, and different chemical reactions occurred. Titanium carbide with minor vanadium alloying (Ti,V)C reaction products act as diffusion barriers when using PCD and cemented carbide, while the reaction products acting as diffusion barrier in pcBN is (Ti,V)B2. The presence of Mo and W in binder sites of pcBN reduces diffusional dissolution of cBN. Diffusion simulations agreed well with microscopy investigations and were enabled by the known temperature and pressure conditions of the static diffusion couples.

Cemented carbides are metallic composites consisting of a WC hard phase and a ductile binder, usually Co-based, produced by powder metallurgy and sintering. Cemented carbides are an essential part of modern material and manufacturing processes. However, Co powder is classified as a carcinogenic material with serious health hazards, and most virgin Co reservoirs are located in conflict regions. In addition, there are monopolies in the market for pure tungsten. Therefore, reducing the consumption of cobalt or replacing it with other non-hazardous elements would increase the sustainability of cemented carbide production. Furthermore, advances in production technology can help overcome raw material limitations. One such advancement is non-homogeneous structures and properties for optimization of microstructure which is the topic of this thesis. 

Integrated computational materials engineering (ICME) and its complementary tools, calculation of phase diagram (CALPHAD), and ab-initio modeling are strong tools that bridge experimentation and modeling. In this thesis, a framework for the material design of non-homogeneous cemented carbides is proposed and tested using these computational tools. 

The workflow of the material design of non-homogeneous microstructure and properties were studied on different length scales. Atomistic modeling with density functional theory (DFT), ab-initio molecular dynamics (AIMD), and generalized hydrodynamics (GHD) were used to model the viscosity of liquid Co binder. In addition, the mobility of Ti and Fe in disordered BCC TiFe alloy was assessed using new experimental data from the diffusion couple experiments and an electron probe micro-analyzer (EPMA). These two studies were conducted to complete the data necessary to study cemented carbides’ processing and performance. 

The other studied phenomenon studied by experimentation and modeling is the formation of the gradient zone and the γ cone structure. In addition, a phenomenological model for liquid phase migration (LPM) was created and implemented using the homogenization approach. The LPM pro- cess was studied experimentally and modeled with the YAPFI software. A study of these performers was necessary to link processing and microstructure. On the performance side, the chemical interaction between cutting tools and Ti alloys was studied in detail through experimentation and modeling of diffusion. In addition, hardness and toughness models were applied to predict the longevity of studied cemented carbides. Finally, by applying ICME and material design, a high entropy alloy (HEA) alternative to Co binder was designed, produced, and tested. 

The research presented in this dissertation attempts to fill the gaps in the material design workflow of cemented carbides by developing new tools and methods based on ICME and CALPHAD paradigms. This goal is achieved by studying different length scales, processing methods, microstructure, properties, and performance of cemented carbides. 

Hårdmetaller är metalliska kompositer som består av en hård fas, oftast WC, och ett segt bindemedel, vanligtvis Co-baserat, framställt genom pulvermetal- lurgi och sintring. Hårdmetaller är en väsentlig del av de flesta produktions- processer. Emellertid är Co-pulver klassificerat som ett cancerframkallande material med allvarliga hälsorisker, och de flesta jungfruliga Co-reservoarer finns i konfliktområden. Dessutom finns det monopol på marknaden för ren volfram. Därför skulle en minskning av förbrukningen av kobolt eller att ersät- ta den med andra ofarliga ämnen öka hållbarheten i produktionen av hårdme- tall. Dessutom kan framsteg inom produktionsteknik hjälpa till att övervin- na råvarubegränsningar. Ett sådant framsteg är “icke-homogena” strukturer och beräkiningsverktyg för optimering av produktmikrostruktur som är äm- net för denna avhandling. “Integrated Computational Materials Engineering (ICME)” och dess komplementärar verktyg, beräkning av fasdiagram (CALP- HAD) och ab-initio modellering, är verktyg som överbryggar experiment och modellering. Med hjälp av dessa verktyg föreslås och testas ett ramverk för materialdesign av icke-homogena hårdmetaller i denna avhandling.

Arbetsflödet för materialdesign av icke-homogen mikrostruktur och egen- skaper studerades påolika längdskalor. Atomistisk modellering med densitets- funktionsteori (DFT), ab-initio molekylär dynamik (AIMD) och generaliserad hydrodynamik (GHD) användes för att modellera viskositeten hos flytande Co-bindemedel. Rörligheten för Ti och Fe i oordnad BCC TiFe utvärderades med hjälp av nya experimentella data som samlats in från diffusionsparexpe- rimentet och EPMA-analys. Dessa två studier syftade till att komplettera de data som är nödvändiga för att studera hårdmetalls bearbetning och prestan- da. Bildandet av gradientzonen och γ-konstrukturen modellerades och utvär- derades experimentellt. En fenomenologisk modell för flytande fasmigrering (“ Liquid Phase Migration”, LPM) skapades och implementerades med hjälp av homogeniseringsmetoden. LPM-processen studerades experimentellt och mo- dellerades med YAPFI-mjukvaran. En studie av dessa processer var nödvän- dig för att koppla samman bearbetning och mikrostruktur. På prestandasidan studerades kemisk interaktion mellan skärverktyg och Ti-legeringar i detalj genom experiment och diffusionsmodellering. Dessutom användes hårdhets- och seghetsmodeller för att förutsäga hårdmetallers prestanda. Slutligen, med tillämpning av ICME och materialdesign, designades, producerades och tes- tades ett alternativt bindemedel med bestående av högentropilegering. ICME och CALPHAD genomsyrade hela forskningsprojekted. Studierna på olika längdskalor hjälpte till att bättre förstå bearbetning, mikrostruktur, egenska- per och prestanda hos hårdmetaller. Dessutom har nya verktyg och metoder utvecklats för att fylla luckorna i materialdesignens arbetsflöde för hårdme- taller.

Hårdmetaller är metalliska kompositer som består av en hård fas, oftast WC, och ett segt bindemedel, vanligtvis Co-baserat, framställt genom pulvermetal- lurgi och sintring. Hårdmetaller är en väsentlig del av de flesta produktions- processer. Emellertid är Co-pulver klassificerat som ett cancerframkallande material med allvarliga hälsorisker, och de flesta jungfruliga Co-reservoarer finns i konfliktområden. Dessutom finns det monopol på marknaden för ren volfram. Därför skulle en minskning av förbrukningen av kobolt eller att ersät- ta den med andra ofarliga ämnen öka hållbarheten i produktionen av hårdme- tall. Dessutom kan framsteg inom produktionsteknik hjälpa till att övervin- na råvarubegränsningar. Ett sådant framsteg är “icke-homogena” strukturer och beräkiningsverktyg för optimering av produktmikrostruktur som är äm- net för denna avhandling. “Integrated Computational Materials Engineering (ICME)” och dess komplementärar verktyg, beräkning av fasdiagram (CALP- HAD) och ab-initio modellering, är verktyg som överbryggar experiment och modellering. Med hjälp av dessa verktyg föreslås och testas ett ramverk för materialdesign av icke-homogena hårdmetaller i denna avhandling.

Arbetsflödet för materialdesign av icke-homogen mikrostruktur och egen- skaper studerades påolika längdskalor. Atomistisk modellering med densitets- funktionsteori (DFT), ab-initio molekylär dynamik (AIMD) och generaliserad hydrodynamik (GHD) användes för att modellera viskositeten hos flytande Co-bindemedel. Rörligheten för Ti och Fe i oordnad BCC TiFe utvärderades med hjälp av nya experimentella data som samlats in från diffusionsparexpe- rimentet och EPMA-analys. Dessa två studier syftade till att komplettera de data som är nödvändiga för att studera hårdmetalls bearbetning och prestan- da. Bildandet av gradientzonen och γ-konstrukturen modellerades och utvär- derades experimentellt. En fenomenologisk modell för flytande fasmigrering (“ Liquid Phase Migration”, LPM) skapades och implementerades med hjälp av homogeniseringsmetoden. LPM-processen studerades experimentellt och mo- dellerades med YAPFI-mjukvaran. En studie av dessa processer var nödvän- dig för att koppla samman bearbetning och mikrostruktur. På prestandasidan studerades kemisk interaktion mellan skärverktyg och Ti-legeringar i detalj genom experiment och diffusionsmodellering. Dessutom användes hårdhets- och seghetsmodeller för att förutsäga hårdmetallers prestanda. Slutligen, med tillämpning av ICME och materialdesign, designades, producerades och tes- tades ett alternativt bindemedel med bestående av högentropilegering. ICME och CALPHAD genomsyrade hela forskningsprojekted. Studierna på olika längdskalor hjälpte till att bättre förstå bearbetning, mikrostruktur, egenska- per och prestanda hos hårdmetaller. Dessutom har nya verktyg och metoder utvecklats för att fylla luckorna i materialdesignens arbetsflöde för hårdme- taller.

Understanding diffusion-induced isothermal solidification time during transient liquid phase bonding is vital in producing intermetallic-free robust joints. The isothermal solidification completion time is overestimated by the existing analytical models, even by the closest one to the real bonding conditions, known as the moving interface model. It was found that the boride formation in the diffusion affected zone of Ni-based superalloy upon using B-containing filler metals is one of the reasons behind the inability of the moving interface model to predict the isothermal solidification completion time accurately, which has received scant attention in the literature. Moreover, simplified assumptions in deriving the moving interface model such as constant interfacial solute concentration, which is only valid for binary systems, along with the independency of diffusion coefficient to concentration introduce errors when estimating the isothermal solidification time using the moving interface model. The significant discrepancy between the predicted and experimentally obtained isothermal solidification times reinforces the idea that the existing moving interface analytical model needs to be modified.

Pure titanium has an HCP structure and lacks mechanical properties for many industrial purposes. The BCC phase of Ti is required to make alloys with increased strength compared to pure Ti. Iron is the most potent element for stabilising the BCC phase. However, the addition of Fe to Ti causes segregation issues during solidification, which can be avoided by diffusion-driven solid-state alloying. To predict the diffusion kinetics, the interaction mobility parameters of Ti and Fe in the disordered BCC phase of Ti are necessary. In this work, these parameters are optimised based on new experimental data from Ti-Fe diffusion couples produced by the Field Assisted Sintering Technology (FAST). Diffusion couples were held at 1173K and 1273K for one hour. High-resolution Fe concentration profiles are obtained from Electron Probe Micro Analyser (EPMA). Ternary mobility interaction parameters are assessed based on binary endmembers with a DICTRA sub-module, and results are compared to earlier assessments of mobilities of the disordered BCC TiFe system.

Cemented carbides with mesoscopically non-homogeneous properties by design represent a potential to enhanceperformance in metal cutting and rock drilling. Development of in-homogeneous structured hard materialsthrough an ICME approach requires a thorough understanding of diffusion kinetics during solid and liquid statesintering. In this work, we used thermodynamics and diffusion kinetics modelling tools to predict the micro-structure and resulting properties of cemented carbide composites. First, we designed and gradient sintered two(WC-TiCN-Co) cemented carbides with different nitrogen to titanium ratios. Second, we reproduced the experi-mental results in 2D by means of thermodynamic and kinetic simulations. In the last step we calculated fracturetoughness KIC, and Vickers hardness of cemented carbides. The agreement between simulations and experimentalresults is fair and acceptable

Cemented carbide, also known as hard metal, is one of the most outstanding composite engineering materials since its commercial introduction in the 1920s. The unique combination of strength, hardness and toughness makes cemented carbides highly versatile materials for the most demanding engineering applications. In their simplest form, these materials are composites of tungsten carbide (WC) grains that are cemented with a ductile metallic binder phase, typically cobalt. However, despite the superiority of Co as binder material, there is a long-standing need to find alternative binders due to serious health concerns that have haunted the industry for nearly 80 years. In the present study, we develop a new cemented carbide with a high entropy alloy binder phase (CoCrFeNi) from raw materials to a fully functional, coated and gradient-sintered cutting tool insert. The new hard metal with reduced Co content is designed by using first principles theory and the CALPHAD method. The cutting tool was made by pressing the new hard metal in a standard geometry, sintered to have a thin binder phase enriched surface zone, free from cubic carbides and coated with protective layers of Ti(C,N) and Al2O3. The resulting cutting insert was tested in a real machining operation and compared to a state-of-the-art reference that had Co as binder phase. The cutting tool made of the newly developed cemented carbide has an exceptionally high resistance against plastic deformation at all tested cutting speeds in the machining test, outperforming the reference insert, which shows a linear increase in edge depression when the cutting speed is increased. This result opens up the possibility to utilize the unique properties of high entropy alloys for industrial applications, in particular, as binder phase in new cemented carbides.