Mingzhi Xu

• Doctor of Philosophy
• Professor (Assistant) at Georgia Southern University

Solidification and cooling of a hypoeutectic gray cast iron were interrupted at various stages by quenching the iron sampled with custom-made quartz molds in an iced brine. Microstructure evolution of the gray iron was interrupted and retained by quenching. A scanning electron microscope equipped with energy-dispersive X-ray spectrometry and automa...

A bottom-filled rigging system was designed to produce gray iron castings, which was compared with a top-filled design in the present study. Filling and solidification of gray iron produced with the bottom-filled mold were compared with that for the top-filled mold. At similar cooling rate and solidification condition, the count of Type A graphite...

Fineness of microstructural constituents in the metallic alloys affects their mechanical properties. This study sought to determine the effects of selected levels of titanium, cerium and aluminum on the fineness of microstructural constituents within ductile iron. A hypoeutectic iron was studied. Cerium additions in the amounts of 0.01 wt.% and 0.0...

Fast removal of soft phases (e.g., pearlite and ferrite) in the iron matrix limits the wear life of high-Cr white irons. To address this shortcoming, the authors successfully produced fine networks of M6C carbide in a high-Cr white iron through extensive thermodynamic calculations. Fishbone-like networks of M6C carbides were observed with an optica...

An Fe-15Mo-18Cr-3.3C-1.65V white iron has been widely used in industries for many years due to its excellent wear performance, but never been reported to academic circle. This paper studied its phase constituents in as-cast condition and its wear performance for metal-to-metal contact wear applications. Microstructural analyses were performed using...

The efficiency of removal of solid alumina inclusions by filtration and the distribution of inclusions captured through the thickness of the filter was investigated for an aluminum killed 316 stainless steel casting. A mold design was developed using modeling software to produce two castings that fill simultaneously, one with a filter and the other...

Frictional heat-induced severe adhesive wear has been limiting the lifetime of metal-to-metal wear systems for many years. Five graphitic white irons were previously designed and produced to introduce flake graphite into white iron, with the goal to expedite heat dissipation and reduce the frictional heat effect. This paper focused on the graphite...

The complex nature of nodular graphite nuclei was studied in a partially solidified and quenched spheroidal graphite iron (SGI) that contained small graphite nodules. The reduced graphite to nuclei diameter ratio obtained by the accelerated solidification process increased the probability of nuclei exposure during metallographic cross sectioning. T...

Atom probe tomography (APT) with high sensitivity and spatial resolution was applied to study the elemental distributions in spheroidal graphite in ductile iron. A specimen of quenched ductile iron with some graphite nodules in direct contact with liquid phase was used in this study to understand the role of alloying elements in spheroidal graphite...

Non-metallic inclusions are mainly comprised of oxides, sulfides, and nitrides, and are formed in liquid steel during the melting and refining process, as a result of reoxidation, worn-out refractories, or entrained slag. The notch toughness of high strength steels is particularly susceptible to the type, number, size, and distribution of non-metal...

The efficiency of ceramic foam filters in removing different inclusion populations in a Fe–30Mn–9Al–1Si–0.9C–0.5Mo steel was investigated. A mold design was created utilizing fluid flow and solidification modeling software. The design utilized a common pouring cup attached to two different but balanced gating systems. One runner utilized a ceramic...

Es wurde eine Untersuchung durchgeführt, um die Effizienz der Entfernung fester Aluminiumoxideinschlüsse durch Filtration während des Gießens zu messen. Unter Verwendung einer Modellierungssoftware wurde eine Formauslegung entwickelt, um zwei Gussteile herzustellen, die gleichzeitig gefüllt werden; ein Gussteil mit, das andere ohne Filter. Durch di...

Frictional heat generated in high speed sliding and rolling wear generates a significant amount of heat. Metal loses a large portion of hardness at high temperature, making it more susceptible to failures. Temperature rise due to abrasive wear on contact surface is a serious issue that limits the lifetime of many metal-to-metal contact wear systems...

Introducing flake graphite into white iron can enhance the thermal diffusivity of the wear component, which can in turn expedite the heat dissipation and extend service life. The first generation of graphitic white irons were designed, produced and investigated. Thermal diffusivity for studied alloys was measured using a laser flash apparatus follo...

Heat induced adhesive abrasion failure has often been found in metal-to-metal wear application, hence interconnected flake graphite networks were deliberately generated in a white iron to increase its thermal conductivity, which is called graphitic white iron. An alloy with 11.03wt.% Cr was cast and investigated. Solidification sequence was determi...

Cr-Ni-Mo steel was melted using either a high sulfur or a high oxygen practice to control nitrogen pickup aiming to produce cast steel with high strength (>1380 MPa/ 200 ksi) and high hardness (500-560 HBW/ 51-55 HRC). Zirconium or aluminum additions were used for deoxidation. Addition of zirconium (0.02 wt. %) with ZrN formation was found to be pr...

A Mn-Si-Mo-V steel was formulated to minimize solidification shrinkage porosity with the goal of obtaining a high strength and impact resistant steel. Three chemistries viz. Baseline, Baseline plus 2 wt. % Nickel (Ni) and Baseline with 1.5 wt. % Ni but no vanadium (V) were produced keeping a manganese to carbon ratio of 5 to 1. Steels were heat tre...

Metal-to-metal wear systems are widely used in various industries, but heat-induced adhesive wear has been limiting the lifetime of the components for many years. An idea of introducing interconnected flake graphite networks into white iron was developed by the authors, which can potentially solve this problem by increasing the overall thermal cond...

Fused silica is widely used in investment casting shell molds as flour, stucco and binder for its superior properties, such as low linear thermal expansion coefficient and high thermal shock resistance. Investment shell molds are usually fired after the de-wax process to remove the residue pattern material, and to improve shell strength through sin...

Introducing interconnected flake graphite networks into a white iron can potentially reduce thermal induced adhesive abrasion during metal-to-metal contact. Five alloys with different chromium and carbon contents were designed, produced and investigated to develop the first generation of graphitic white iron. The graphite volume percent for each al...

The size distribution and morphology of inclusions in steel products are influenced by plant practices during steelmaking, casting and hot rolling. In this study, the evolution of the size distribution of oxide inclusions during the production of a line pipe steel in a mini mill was investigated. LMF, tundish, mold, and hot rolled coil samples were...

Characterizing Graphite Nodule in Ductile Iron using TKD and TEM - Volume 24 Supplement - Jingjing Qing, Mingzhi Xu

Inclusion size distribution and shape are typically determined from the analysis of a polished cross-section of steel specimen. However, measured inclusion characteristics such as the 2D size distribution and shape can differ from the actual 3D characteristics that influence the mechanical properties of steel. In this study, MnO·SiO2 inclusions tha...

A mold design was developed using mold filling and solidification software to evaluate the efficiency of solid alumina inclusion and liquid manganese silicate inclusion removal by filtration during casting. In this design, two castings fill simultaneously, one with a filter and the other without a filter. The design reduced vortex formation and thu...

An investigation was performed to measure the efficiency of solid alumina inclusion removal by filtration during casting. A mold design was developed using modeling software to produce two castings that fill simultaneously, one with a filter and the other without a filter. The design avoided vortex formation and thus air entrainment, which helped t...

Investigations into the evolution of inclusion populations during ladle processing and continuous casting are reviewed. Details of the steelmaking practices employed in BOP and EAF steelmaking have been observed to have a strong influence on the size distribution, quantity, composition, phases and morphology of the final inclusion population delive...

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The effect of moisture diffusion on the mechanical properties of carbon/bismaleimide composites exposed to seawater conditioning at elevated temperatures was investigated in this study. Carbon/bismaleimide composites with two stacking sequences (unidirectional and cross-ply) were fabricated using out-of-autoclave process. Testing coupons were immer...

Photopolymer-based stereo-lithography (SL) rapid prototyping patterns with honeycomb internal structure reduce lead time and material cost for pattern manufacturing and also minimize ceramic mold residue after pattern removal in investment casting process. However, relatively larger thermal expansion of SL pattern tends to cause ceramic shell crack...

Reliable and realistic thermal properties data for investment casting shell molds are required to correctly simulate the solidification and predict the shrinkage. Investment casting shells exhibit several phase transformations during firing and pouring which affect their transient thermal properties. These properties are dependent upon time, temper...

Process of photopolymer stereo-lithography (SLA) provides a unique opportunity for rapid prototyping of high surface quality and complex geometry investment castings from ferrous and non-ferrous metals. A specific internal honeycomb structure gives a combination of high pattern stiffness needed for precise replication of geometry by investment shel...

This study presents determination on the thermal properties of investment casting shell molds used in casting process modeling. Superheat and latent heat from solidification and cooling of a casting can either be accumulated by ceramic shell for thin-walled casting or transfer to environment for massive casting. Heat capacity and thermal conductivi...

The applicability of different low density rigid polymer pattern materials for investment casting process was experimentally investigated. The studied materials included polymer foam of different densities and compositions as well as SLA polymer patterns with internal honeycomb structure produced by stereolithography. Densities and elastic moduli o...

To verify the feasibility of efficiently fabricating Al/steel corrosion-resistant bimetal composite by the authors' friction stir brazing (FSB) process, in which a tool without probe is used to eliminate severe wear of probe by steel, the characteristics of bead surface forming, interfacial microstructure and property of FSB joint of Al/steel were...