CN1676250A

CN1676250A - Nano zirconium oxide plasma activation sintering method

Info

Publication number: CN1676250A
Application number: CN 200510052090
Authority: CN
Inventors: 彭金辉; 张世敏; 马骏骑; 张利波; 杨显万; 华一新; 朱祖泽; 何蔼平; 王�华; 李荣兴
Original assignee: Kunming University of Science and Technology
Current assignee: Kunming University of Science and Technology
Priority date: 2001-01-20
Filing date: 2001-01-20
Publication date: 2005-10-05
Anticipated expiration: 2021-01-20
Also published as: CN1292863C

Abstract

The present invention relates to a nano zirconium oxide plasma activating and sintering method. Said sintering process can be implemented by four stages: first stage, applying coaxial pressure to nano zirconium oxide material granules; second stage, retaining constant pressure, applying pulse voltage, producing plasma and activating nano zirconium oxide material granule surface; third stage; turning off the pulse power supply circuit, under the action of constant pressure using direct current to heat nano zirconium oxide to required temperature and time; and fourth stage, stopping heating, eliminating pressure so as to obtain the finished product. Said invention also provides the concrete parameter requirement for implementing said instering process.

Description

A kind of method of nano zirconium oxide plasma activation sintering

One, technical field: a kind of powdered metallurgical material preparation, processing technology.

Two, background technology: sintering is one of operation the most basic in the powder metallurgy production process.Sintering is a high temperature action, generally will also suitable protective atmosphere will be arranged through the long time.Therefore, consider from economic angle that the consumption of sintering circuit is the pith that constitutes product cost, improves operation and agglomerating plant, reduces the consumption of material and energy, as reducing sintering temperature, shortening sintering time etc., meaning economically is very big.

Known sintering method has: traditional pressureless sintering method, hot pressing sintering method, microwave sintering method, plasma sintering method (as microwave plasma, direct-current plasma) but all have outside its deficiency.No matter long, poor, the energy consumption height of properties of product of tradition pressureless sintering method process time adopts the fuel heating still to adopt electrical heating, all makes cost up, is therefore replaced by some novel sintering methods gradually.Though hot pressing sintering method has adopted pressure, in the sintering process activation degree (being dynamic process) of sample still needed and further improve, and apparatus expensive and process-cycle are long.And microwave sintering method and plasma sintering method are improved aspect activation, shortened sintering time, reduced sintering temperature, suppressed growing up of dusty material particle, but experimental condition such as temperature is difficult to control in the sintering process, particularly cause the thermal runaway effect easily in the microwave sintering process, dusty material is produced inhomogeneous heating, thereby influenced the various performances of sintered products, thereby a kind of new method that can improve above-mentioned sintering process shortcoming of in the preparation of dusty material and process, still needing.

Plasma activated sintering dusty material technology, abroad start to walk since the nineties, because it melts plasma-activated, hot pressing, resistance heated is an one, have advantages such as sintering time weak point, temperature precise control, the relative theory density that only in minutes just makes dusty material is near 100%, and can effectively improve the various performances of material, thereby the research of plasma activated sintering and being applied in abroad emerges rapidly, becomes the new focus of dusty material research.

What essential distinction do plasma activated sintering and plasma sintering have so? plasma sintering is placed on material in the plasma atmosphere and carries out, and mainly contains the discharge of direct current cathode cavity, high-frequency induction, three kinds of methods that produce high-temperature plasma of microwave-excitation at present.The device that these three kinds of methods adopt all has a cover to keep the system of vacuum and control gas pressure and flow, and different mainly is the power mode that produces plasma.The essence of this technology is that the high-temperature plasma of utilize producing heats material, and the heat exchange by material and high-temperature plasma realizes sintering, promptly plasma as thermal source, material is carried out sintering.But shortcoming is: sample is easy to generate cracking, and along with the rising of temperature, the volatilization of material also aggravates, and technology and theory are all immature.

And the plasma activated sintering method is the micro discharge phenomenon of utilizing between powder particle that the gap produced, by the plasma strike and the intergranular contact portion of heating powder of discharging and being produced, can make the material of contact portion produce evaporation, thereby reach the purpose of purification and activated powder particle, have advantages such as sintering time weak point, temperature precise control, easy industrialization.

Three, summary of the invention: the present invention is needing to impose pulse voltage on the dusty material of sintering, produce plasma with activated powder material granule surface, by direct current the dusty material Fast Heating is heated up, exert pressure again with sintering and curing powder material, it is even to reach that sintering time is short, the temperature precise control is sintered material granule, improves the purpose of material property.

Fig. 1 is the installation drawing of plasma activated sintering of the present invention, and 1 is Pulased power supply unit among the figure, the 2nd, and resistive heating device, the 3,4,5,6,11, the 12nd, the axial pressure device, the 10th, the sintering mould, 9 and 13 is upper and lower drifts.The dusty material that needs sintering is placed the sintering mould and imposes homoaxial pressure, in dusty material, produce the particle surface of plasma with pulse voltage with activated material, be heated by resistive device then and impose direct current, material is carried out Fast Heating, to finish activated sintering to dusty material.(the plasma activated sintering device is described in the utility application that the applicant proposes on January calendar year 2001 13).

Fig. 2 is temperature, the pressure schematic diagram of above-mentioned sintering process four-stage.Sintering divides four-stage to carry out: the phase I, the dusty material that is sintered is slightly executed homoaxial pressure; Second stage keeps constant pressure, and adds pulse voltage, produces plasma, and particle surface is activated, and supervenes a spot of heat; Phase III, close pulse power supply circuit, continue to improve pressure, under the constant voltage effect, be heated to temperature required and the time to material with direct current; The quadravalence section stops the D.C. resistance heating, eliminates pressure.Applied pressure, temperature and pulse voltage need to decide according to the dusty material and the sintered products performance that are sintered.

Fig. 3 is Pulased power supply unit and resistive heating device circuit theory diagrams

Become Rectified alternating current, obtain HVDC after by capacitor filtering through three-phase bridge rectification by the three phase sine alternating current, this high voltage direct current is sent into the power switch inverter, become the square wave alternating current, transfer grand to required voltage through intermediate-frequency transformer, behind switching and rectifying, inductor filter, can obtain working direct current again.It is that a kind of contravariant external characteristics is that voltage falls suddenly, the constant-current type electric current.

For guaranteeing the constant set-point of direct current of resistive heating device output, in Circuits System, be provided with current regulation control circuit and Current Feedback Control circuit in technological requirement; For the pulse direct current that guarantees Pulased power supply unit output satisfies technological requirement, be provided with the modulator loop that pulse frequency modulation and pulse-width modulation circuit constitute especially, in order to the low frequency dc pulse voltage is modulated on the direct current of output.

Pulased power supply unit, resistive heating device, desired parameters will generally can be controlled in according to the difference of agglomerated material and sintered products performance requirement is set during the work of axial pressure device: (1) pulse voltage 5～100V, pulse current 100～250A, pulse turn-on time 10～90ms, pulse 10～80ms breaking time, overall pulse time 20～100s; (2) resistance heated voltage 5～120V, electric current 100～1200A, power-efficient are greater than 80%, and power factor (PF) is greater than 0.9; (3) temperature range is 200～1600 ℃.

Compare advantage and good effect that the present invention has with known technology:

(1) to the dusty material pressurization accurately, steadily controlled;

(2) Pulased power supply unit and resistive heating device stability is high, continuity is good, and adjustable extent is big, and dynamic response is fast;

(3) owing to the activation of plasma, new technology can realize low-temperature sintering, has so just suppressed growing up of crystal grain, from having improved the performance of sintered body in essence.

(4) sintering time is short, compares with the several hrs of conventional sintering, has saved the energy, has reduced the loss of equipment.

This technology also can make up configuration respectively with Medium frequency induction or AC resistance stove, also can carry out plasma-activated-Medium frequency induction sintering, plasma-activated-indirect resistance heat-agglomerating etc.

This technology also can be used for exploring the activated sintering of different types of dusty material or the different process process of preferred dusty material of the same race, also can adopt first activation, after the technical process such as knot of pressurizeing, reburn.

Four, description of drawings: Fig. 1 is an installation drawing of the present invention, and 1 is Pulased power supply unit among the figure, the 2nd, and resistive heating device, the 3,4,5,6,11, the 12nd, the axial pressure device, the 10th, the sintering mould, 9 and 13 is upper and lower drifts.Fig. 2 is temperature, the pressure schematic diagram of sintering process quadravalence section.Fig. 3 is Pulased power supply unit and resistive heating device circuit theory diagrams.

Five, the specific embodiment:

Embodiment 1: the plasma activated sintering of alumina in Nano level

Packed in the sintering mould in the nano-alumina powder end, at first powder is activated with pulse current, be rapidly heated subsequently and powder exerted pressure and carry out sintering, pulse current 850A wherein, pulse turn-on time 60ms, breaking time 30ms, plasma-activated time 90s, pressure 40Mpa, 1250～1300 ℃ of heating-up temperatures.

Embodiment 2: the plasma activated sintering of Hardmetal materials WC+Co

With purity is that 99.9% WC powder and purity are to pack into after 99.8% Co powder evenly mixes in proportion in the sintering mould, at first powder is activated with pulse current, be rapidly heated subsequently and powder exerted pressure and carry out sintering, the process conditions of sintering need be followed according to the percentage composition of Co powder in the alloy and be set.

(a), to the optimum process condition of WC-6%Co dusty material sintering: pulse current 600A, pulse turn-on time 40ms, plasma-activated time 30s, pressure is 30.5Mpa, 1350 ℃ of following sintering 5 minutes, hardness reached HRA92, and the relative theory density value is 99.83%.

(b), to the optimum process condition of WC-10%Co dusty material sintering: pulse current 500A, pulse turn-on time is 40ms, be 60ms breaking time, the plasma-activated time is 25s, pressure is 26.3Mpa, and heating-up temperature 300-1350 ℃, sintering time is 4 minutes, relative theory density reaches 99.65%, and Rockwell hardness reaches 91.

(c), to the optimum process condition of WC-15%Co dusty material sintering: pulse current 450A, pulse turn-on time is 40ms, be 60ms breaking time, the plasma-activated time is 20s, pressure is 21.6MPa, 1300 ℃ of following sintering 5 minutes, hardness reached HRA90, and the relative theory density value is 99.90%.

(d), to the optimum process condition of WC-20%Co dusty material sintering: pulse current 400A, pulse turn-on time is 20ms, be 80ms breaking time, the plasma-activated time is 30s, heating-up temperature 1250-1300 ℃, pressure was 17.6Mpa, 1300 ℃ of following sintering 5 minutes, hardness reaches HRA89, and the relative theory density value is 99.93%.

Embodiment 3: nanoscale ZrO ₂High beta plasma activated sintering

With nanoscale ZrO ₂Powder is packed in the sintering mould, at first with pulse current powder is activated, be rapidly heated subsequently and powder exerted pressure and carry out sintering, optimum process condition is: pulse current 700A, pulse turn-on time 45ms, breaking time 30ms, plasma-activated time 60s, pressure 30Mpa, heating-up temperature 1300-1400 ℃, sintering time is 7 minutes, and Vickers hardness reaches 15.4Gpa, and relative theory density is near 100%.

The plasma activated sintering of embodiment 4:Cu powder

Technological parameter is: pulse current 2500A, pulse turn-on time are that 40ms, breaking time are 60ms, adopt D.C. resistance heat-agglomerating to 600 ℃ again, total activated sintering time is 15s, reduce to room temperature subsequently, institute's applied pressure is 5MPa in the process, after activated sintering, the solid density of sample reaches 99.6%, and the process time only is 15s.

Claims

1, a kind of method of nano zirconium oxide plasma activation sintering, sintering divide four-stage to carry out, and the phase I, the nano zircite material granule are applied pressure homoaxial with it; Second stage keeps constant pressure, and adds pulse voltage, produces plasma, and nano zircite material granule surface is activated; Phase III, close pulse power supply circuit, under the constant voltage effect, be heated to temperature required and the time to nano zircite with direct current; The quadravalence section, stop the D.C. resistance heating, eliminate pressure, obtain finished product, it is characterized in that: control impuls electric current 700A, pulse turn-on time 45ms, breaking time, 30ms was heated to 1300～1400 ℃ with direct current to nano zircite, and sintering time is 7 minutes, total soak time 60s, pressure 30Mpa.