Exchange Competition, Entry, and Welfare

We assess the consequences for market quality and welfare of different entry regimes and exchange pricing policies. To do so, we integrate a microstructure model with a free-entry, exchange competition model where exchanges have market power in technological services. Free-entry delivers superior liquidity and welfare outcomes vis-`a-vis an unregulated monopoly, but entry can be excessive or insufficient. Depending on the extent of the monopolist's technological services undersupply compared to the first best, a planner can achieve a higher welfare controlling entry or platform fees.

A novel physics-based and data-supported microstructure model for part-scale simulation of laser powder bed fusion of Ti-6Al-4V

The elasto-plastic material behavior, material strength and failure modes of metals fabricated by additive manufacturing technologies are significantly determined by the underlying process-specific microstructure evolution. In this work a novel physics-based and data-supported phenomenological microstructure model for Ti-6Al-4V is proposed that is suitable for the part-scale simulation of laser powder bed fusion processes. The model predicts spatially homogenized phase fractions of the most relevant microstructural species, namely the stable $$\beta $$ β -phase, the stable $$\alpha _{\text {s}}$$ α s -phase as well as the metastable Martensite $$\alpha _{\text {m}}$$ α m -phase, in a physically consistent manner. In particular, the modeled microstructure evolution, in form of diffusion-based and non-diffusional transformations, is a pure consequence of energy and mobility competitions among the different species, without the need for heuristic transformation criteria as often applied in existing models. The mathematically consistent formulation of the evolution equations in rate form renders the model suitable for the practically relevant scenario of temperature- or time-dependent diffusion coefficients, arbitrary temperature profiles, and multiple coexisting phases. Due to its physically motivated foundation, the proposed model requires only a minimal number of free parameters, which are determined in an inverse identification process considering a broad experimental data basis in form of time-temperature transformation diagrams. Subsequently, the predictive ability of the model is demonstrated by means of continuous cooling transformation diagrams, showing that experimentally observed characteristics such as critical cooling rates emerge naturally from the proposed microstructure model, instead of being enforced as heuristic transformation criteria. Eventually, the proposed model is exploited to predict the microstructure evolution for a realistic selective laser melting application scenario and for the cooling/quenching process of a Ti-6Al-4V cube of practically relevant size. Numerical results confirm experimental observations that Martensite is the dominating microstructure species in regimes of high cooling rates, e.g., due to highly localized heat sources or in near-surface domains, while a proper manipulation of the temperature field, e.g., by preheating the base-plate in selective laser melting, can suppress the formation of this metastable phase.

A numerical investigation on the effects of porosity on the plastic anisotropy of additive manufactured stainless steel with various crystallographic textures

For additive manufacturing materials, different process parameters might cause non-negligible microstructural defects. Due to the deficient or surplus energy input during the process, porosity would result in significantly different mechanical responses. In addition, the heterogeneity of the microstructure of additive manufactured material could increase the anisotropic behavior in both deformation and failure stages. The aim of this study is to perform a numerical investigation of the anisotropic plasticity affected by the microstructural features, in particular, texture and porosity. The coupling of the synthetic microstructure model and the crystal plasticity method is employed to consider the microstructural features and to predict the mechanical response at the macroscopic level, including both flow curve and r-value evolution. The additive manufactured 316L stainless steel is chosen as the reference steel in this study. Porosity decreases the stress of material, however, it reduces the anisotropy of material with both two types of textures. Regardless of porosity, grains with <111>//BD fiber of reference material is preferable for high strength requirement while the random orientations are favorable for homogeneous deformation in applications.

Modeling Static Recrystallization in Al-Mg Alloys

In the present work, the influence of Mg on recrystallization kinetics in Al is analyzed by computer simulation. A comprehensive state parameter-based microstructure model is developed, which describes recrystallization in terms of nucleation and growth. The mechanism of solute drag is fully incorporated, thus accounting for the decrease of grain boundary mobility in the presence of impurity atoms. On the basis of the present approach, the solute binding energy between Mg atoms and grain boundaries is assessed and compared to experimentally measured values. Furthermore, the influence of Mg on dislocation production during strain hardening is modeled. The simulations of the composition and temperature-dependent recrystallization kinetics are verified on experimental studies where excellent agreement is achieved. Both simulation and experiment show that increasing Mg content first decelerates and, later on, accelerates recrystallization kinetics.