Spark plasma sintering the spark-erosion powders of functional alloys

Various shape memory alloys (Ti-Ni-Hf, Ni-Al and Cu-Al-Ni) were elaborated by spark plasma sintering method from the micron, submicron and nano- sized particles prepared by spark-erosion method in cryogenic liquid from preliminary melted master alloys. These alloys are being developed as one of the alternatives for the intermediate temperature applications (100-900oC). Spark plasma sintering method is express method, which provides lower temperature and shorter holding time of sintering. It makes possible to sinter materials from the pre-alloyed powders and eliminate the intensive grains growth and precipitating processes influencing the mechanical and functional properties of functional materials. The effects of processing parameters on the martensitic transformation and microstructure of the sintered compacts were investigated using XRD and SEM study. Temperatures of sintering were chosen according to the assessed data of the decomposition, oxidation and others processes carrying out in material. Although the precipitating processes were usually not completely depressed, the intensive grain growth was also not found in most cases. Most of the microstructure peculiarities of as processed powder were inherited by the sintered material. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2079

The Role of Nano-sized Fraction on Spark Plasma Sintering the Pre-Alloyed Spark-Erosion Powders

Ti-Ni-Hf, Ni-Al and Cu-Al-Ni shape memory materials were produced by spark plasma sintering method from the micron and nano-sized particles prepared by spark-erosion method in cryogenic liquid from preliminary melted master alloys. The effects of spark plasma sintering processing parameters on the martensitic transformation and microstructure of the sintered compacts were investigated using XRD and SEM methods. Although precipitating processes were usually not completely depressed, the intensive grain growth was also not found in most cases. Most of the microstructure peculiarities of as processed powder were inherited by the sintered material. The contradictory role of the nano-sized fraction of powders is discussed: in most case this fraction promotes the rapid sintering but also the oxidation proceses in sintered compacts. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2489

Microstructure Investigation of the Spark Plasma Sintered Cu—Al—Ni Shape Memory Material

Исследована микроструктура компактов Cu—13,0Al—3,9Ni—0,4Ti—0,2Cr масс.%, спечённых плазменно-искровым методом из электроэрозионных порошков, изготовленных из мастер-сплава в жидком аргоне.Досліджено мікроструктуру компактів Cu—13,0Al—3,9Ni—0,4Ti—0,2Cr ваг.% спечених плазмово-іскровим методом із електроерозійних порошків, виготовлених із мастер-стопу в рідкому арґоні.The microstructure of Cu—13.0Al—3.9Ni—0.4Ti—0.2Cr wt.% compacts sintered by spark plasma method from powders prepared by spark-erosion method in liquid argon from master alloy is investigated

Influence of the presence of a fluxing agent and its composition on the spectral characteristics of ZnS(Cu) obtained by self-propagating high-temperature synthesis

Investigated in this work were the photoluminescence spectra and luminescence excitation spectra of powered ZnS:Cu, obtained using the method of selfpropagating high-temperature synthesis (SHS) with addition of NaCl and MgCl₂ as a fluxing agent into the charge and without them. It was shown that increasing the amount of fraction with the particle sizes ≤5 nm in powdered ZnS:Cu-SHS, where fluxing agents are present in the charge, is caused by the decrease in temperature inside the reactor in the course of the synthesis reaction. Besides, related increasing the intensity of the PL blue band with λmax ~ 450…465 nm in powdered ZnS:Cu-SHS/MgCl₂, which is associated with redistribution of the copper impurity in the bulk of microcrystals, probably, occurring as a result of increasing the partial pressure of Cl during synthesis

Mechanical Testing of the Shape-Memory Materials Synthesized by a Plasma-Spark Method

Испытания на сжатие были выполнены при комнатной температуре для образцов сплавов Ni49,0—Mn28,5—Ga22,5 (ат.%) и Ni63—Al37 (ат.%), как для выплавленных, так и полученных плазменно-искровым методом (ПИМ). Для обеих систем пластичность ПИМ-образцов возрастает более чем на порядок по сравнению с исходными. Прочность на сжатие сплава Ni—Mn—Ga увеличивается от 180—240 МПа для выплавленных образцов до 510—815 МПа для ПИМ-образцов в зависимости от режимов обработки, для сплава Ni—Al – от 760 до 1310 МПа. Напряжение разрушения образцов Ni—Mn—Ga увеличивается от 185—215 до 1170 МПа, а для образцов Ni—Al – от 790 до 1870 МПа. Спечённые образцы обеих систем имеют композитную структуру, образованную из металлических частиц микронных размеров, скреплённых связующей фазой, состоящей из Ni₃Al и Al₂O₃ для сплава Ni—Al и из MnO с небольшим количеством Ni₃Ga для сплава Ni—Mn—Ga. Предполагается, что эта фаза укрепляет границы зёрен. Это вместе с уменьшением размера зерна, а также многосвязной морфологией образцов Ni—Mn—Ga, консолидированных из полых частиц, и наличием пластической γ′-фазы в частицах Ni—Al улучшает механические свойства сплавов, полученных плазменно-искровым методом.Випробування на стиснення було виконано при кімнатній температурі для зразків стопів Ni49,0—Mn28,5—Ga22,5 (ат.%) та Ni63—Al37 (ат.%), як щойно витоплених, так і одержаних плазмово-іскровою методою (ПІМ). Для обох систем пластичність ПІМ-зразків зростає більш ніж на порядок порівняно із вихідними. Міцність на стиск стопу Ni—Mn—Ga збільшується від 180—240 МПа для щойно витоплених зразків до 510—815 МПа для ПІМ-зразків, залежно від режимів оброблення; для стопу Ni—Al – від 760 до 1310 МПа. Напруження руйнування зразків Ni—Mn—Ga збільшується від 185—215 до 1170 МПа, а для зразків Ni—Al – від 790 до 1870 МПа. Спечені зразки обох систем мають композитну структуру, утворену з металевих частинок мікронних розмірів, пов’язаних сполучною фазою, що складається з Ni₃Al і Al₂O₃ для стопу Ni—Al та з MnO з невеликою кількістю Ni₃Ga для стопу Ni—Mn—Ga. Передбачається, що ця фаза зміцнює межі зерен. Це разом із зменшенням розміру зерна, а також багатозв’язною морфологією зразків Ni—Mn-Ga, консолідованих із порожнистих частинок, та наявністю пластичної γ′-фази в частинках Ni—Al покращує механічні властивості стопів, одержаних плазмово-іскровою методою.Compression tests are carried out at room temperature with the as-cast and spark-plasma sintered (SPS) specimens of Ni49.0—Mn28.5—Ga22.5 (at.%) and Ni63—Al37 (at.%) alloys. For both systems, ductility of the SPS compacts increases more than by one order of magnitude. Compressive strength of Ni—Mn—Ga alloy increases from 180—240 MPa for induction melted specimens to 510—815 MPa for spark-plasma sintered specimens, depending on the regimes of processing, and for Ni—Al alloy, from 760 to 1310 MPa. Fracture stress of Ni—Mn—Ga and Ni—Al specimens raise from 185—215 to 1170 MPa and from 790 to 1870 MPa, respectively. The SEM and XRD investigations reveal that sintered samples of both systems have a composite structure, which contains the micron-size metallic particles bound by the binder phase. This phase consists of Ni₃Al and Al₂O₃ phases in case of Ni—Al alloy and consists of MnO with apparently small amount of Ni₃Ga phase in case of Ni—Mn—Ga alloy. As assumed, this phase strengthens the grain boundaries. This one, in conjunction with reduction of the grain size, the manifold morphology of the Ni—Mn—Ga specimens consolidated from the hollow particles, the presence of extra ductile γ′-phase in Ni—Al particles, provides the enhancing mechanical properties of alloys fabricated by means of the SPS method

Selective introduction of Cu impurity into fine-dispersed ZnS obtained during the process of one-stage synthesis

Abstract Fine ZnS:Cu, obtained by method of self-propagating high-temperature synthesis was investigated. As flux in the mixture NaCl was used, Zn and S were taken in stoichiometric ratio; Cu concentration in charge consisted ~1.5 wt.%. Using SEM data, it was established that obtained ZnS:Cu consists from two fractions—first with particles sizes ~10 μm and more, and other with sizes 50–500 nm. It was established that composition of ZnS:Cu fractions was essentially different. According to EDS data, Cu concentration in particles of fraction with 50–500 nm sizes consists ~2 wt.%, and in particles with sizes ~10 μm and more the presence of Cu was not detected. The reasons that lead to the selective doping of particles in dependence on their size and also the role of NaCl in processes undergoing during synthesis of material are discussed

Luminescent properties of fine-dispersed self-propagating high-temperature synthesized ZnS:Cu,Mg

The influence of magnesium impurities on luminescent properties of ZnS:Cu,Mg using obtained by self-propagating high-temperature synthesis (SHS) has been investigated. Special attention was paid to changes of photoluminescence spectra caused by relaxation processes in ZnS:Cu,Mg-SHS. It was shown that introduction of magnesium into ZnS:Cu-SHS leads to a change in symmetry of ZnS crystal lattice. It leads to relaxation quenching the photoluminescence bands caused by presence of copper impurities in ZnS